app-MAIL-temp/email_handler.py

"""
Handle the email *forward* and *reply*. phase. There are 3 actors:
- contact: who sends emails to alias@sl.co address
- SL email handler (this script)
- user personal email: to be protected. Should never leak to contact.

This script makes sure that in the forward phase, the email that is forwarded to user personal email has the following
envelope and header fields:
Envelope:
    mail from: @contact
    rcpt to: @personal_email
Header:
    From: @contact
    To: alias@sl.co # so user knows this email is sent to alias
    Reply-to: special@sl.co # magic HERE

And in the reply phase:
Envelope:
    mail from: @contact
    rcpt to: @contact

Header:
    From: alias@sl.co # so for contact the email comes from alias. magic HERE
    To: @contact

The special@sl.co allows to hide user personal email when user clicks "Reply" to the forwarded email.
It should contain the following info:
- alias
- @contact


"""
import argparse
import email
import time
import uuid
from email import encoders
from email.encoders import encode_noop
from email.message import Message
from email.mime.application import MIMEApplication
from email.mime.multipart import MIMEMultipart
from email.utils import formataddr, make_msgid, formatdate, getaddresses
from io import BytesIO
from smtplib import SMTPRecipientsRefused
from typing import List, Tuple, Optional

import newrelic.agent
from aiosmtpd.controller import Controller
from aiosmtpd.smtp import Envelope
from email_validator import validate_email, EmailNotValidError
from flanker.addresslib import address
from flanker.addresslib.address import EmailAddress
from sqlalchemy.exc import IntegrityError

from app import pgp_utils, s3
from app.alias_utils import try_auto_create
from app.config import (
    EMAIL_DOMAIN,
    URL,
    UNSUBSCRIBER,
    LOAD_PGP_EMAIL_HANDLER,
    ENFORCE_SPF,
    ALERT_REVERSE_ALIAS_UNKNOWN_MAILBOX,
    ALERT_BOUNCE_EMAIL,
    ALERT_SPAM_EMAIL,
    SPAMASSASSIN_HOST,
    MAX_SPAM_SCORE,
    MAX_REPLY_PHASE_SPAM_SCORE,
    ALERT_SEND_EMAIL_CYCLE,
    ALERT_MAILBOX_IS_ALIAS,
    PGP_SENDER_PRIVATE_KEY,
    ALERT_BOUNCE_EMAIL_REPLY_PHASE,
    NOREPLY,
    BOUNCE_EMAIL,
    BOUNCE_PREFIX,
    BOUNCE_SUFFIX,
    TRANSACTIONAL_BOUNCE_PREFIX,
    TRANSACTIONAL_BOUNCE_SUFFIX,
    ENABLE_SPAM_ASSASSIN,
    BOUNCE_PREFIX_FOR_REPLY_PHASE,
    NEWRELIC_CONFIG_PATH,
    POSTMASTER,
    ALERT_HOTMAIL_COMPLAINT,
    ALERT_YAHOO_COMPLAINT,
)
from app.email import status
from app.email.rate_limit import rate_limited
from app.email.spam import get_spam_score
from app.email_utils import (
    send_email,
    add_dkim_signature,
    add_or_replace_header,
    delete_header,
    render,
    get_orig_message_from_bounce,
    delete_all_headers_except,
    get_spam_info,
    get_orig_message_from_spamassassin_report,
    send_email_with_rate_control,
    get_email_domain_part,
    copy,
    to_bytes,
    send_email_at_most_times,
    is_valid_alias_address_domain,
    should_add_dkim_signature,
    add_header,
    get_header_unicode,
    generate_reply_email,
    is_reply_email,
    normalize_reply_email,
    is_valid_email,
    replace,
    should_disable,
    parse_id_from_bounce,
    spf_pass,
    sl_sendmail,
    sanitize_header,
    get_queue_id,
    should_ignore_bounce,
    get_orig_message_from_hotmail_complaint,
    parse_full_address,
    get_orig_message_from_yahoo_complaint,
)
from app.extensions import db
from app.log import LOG, set_message_id
from app.models import (
    Alias,
    Contact,
    EmailLog,
    User,
    RefusedEmail,
    Mailbox,
    Bounce,
    TransactionalEmail,
    IgnoredEmail,
)
from app.pgp_utils import PGPException, sign_data_with_pgpy, sign_data
from app.utils import sanitize_email
from init_app import load_pgp_public_keys
from server import create_app, create_light_app

# forward or reply
_DIRECTION = "X-SimpleLogin-Type"


_EMAIL_LOG_ID_HEADER = "X-SimpleLogin-EmailLog-ID"
_ENVELOPE_FROM = "X-SimpleLogin-Envelope-From"
_ENVELOPE_TO = "X-SimpleLogin-Envelope-To"

_MIME_HEADERS = [
    "MIME-Version",
    "Content-Type",
    "Content-Disposition",
    "Content-Transfer-Encoding",
]
_MIME_HEADERS = [h.lower() for h in _MIME_HEADERS]

newrelic_app = None
if NEWRELIC_CONFIG_PATH:
    newrelic.agent.initialize(NEWRELIC_CONFIG_PATH)

    newrelic_app = newrelic.agent.register_application()


# fix the database connection leak issue
# use this method instead of create_app
def new_app():
    app = create_light_app()

    @app.teardown_appcontext
    def shutdown_session(response_or_exc):
        # same as shutdown_session() in flask-sqlalchemy but this is not enough
        db.session.remove()

        # dispose the engine too
        db.engine.dispose()

    return app


def get_or_create_contact(from_header: str, mail_from: str, alias: Alias) -> Contact:
    """
    contact_from_header is the RFC 2047 format FROM header
    """
    try:
        contact_name, contact_email = parse_full_address(from_header)
    except ValueError:
        contact_name, contact_email = "", ""

    if not is_valid_email(contact_email):
        # From header is wrongly formatted, try with mail_from
        if mail_from and mail_from != "<>":
            LOG.w(
                "Cannot parse email from from_header %s, use mail_from %s",
                from_header,
                mail_from,
            )
            contact_email = mail_from

    if not is_valid_email(contact_email):
        LOG.w(
            "invalid contact email %s. Parse from %s %s",
            contact_email,
            from_header,
            mail_from,
        )
        # either reuse a contact with empty email or create a new contact with empty email
        contact_email = ""

    contact_email = sanitize_email(contact_email)

    contact = Contact.get_by(alias_id=alias.id, website_email=contact_email)
    if contact:
        if contact.name != contact_name:
            LOG.d(
                "Update contact %s name %s to %s",
                contact,
                contact.name,
                contact_name,
            )
            contact.name = contact_name
            db.session.commit()

        # contact created in the past does not have mail_from and from_header field
        if not contact.mail_from and mail_from:
            LOG.d(
                "Set contact mail_from %s: %s to %s",
                contact,
                contact.mail_from,
                mail_from,
            )
            contact.mail_from = mail_from
            db.session.commit()

        if not contact.from_header and from_header:
            LOG.d(
                "Set contact from_header %s: %s to %s",
                contact,
                contact.from_header,
                from_header,
            )
            contact.from_header = from_header
            db.session.commit()
    else:
        LOG.d(
            "create contact %s for alias %s",
            contact_email,
            alias,
        )

        try:
            contact = Contact.create(
                user_id=alias.user_id,
                alias_id=alias.id,
                website_email=contact_email,
                name=contact_name,
                mail_from=mail_from,
                from_header=from_header,
                reply_email=generate_reply_email(contact_email, alias.user)
                if is_valid_email(contact_email)
                else NOREPLY,
            )
            if not contact_email:
                LOG.d("Create a contact with invalid email for %s", alias)
                contact.invalid_email = True

            db.session.commit()
        except IntegrityError:
            LOG.w("Contact %s %s already exist", alias, contact_email)
            db.session.rollback()
            contact = Contact.get_by(alias_id=alias.id, website_email=contact_email)

    return contact


def get_or_create_reply_to_contact(
    reply_to_header: str, alias: Alias
) -> Optional[Contact]:
    """
    Get or create the contact for the Reply-To header
    """
    try:
        contact_name, contact_address = parse_full_address(reply_to_header)
    except ValueError:
        return

    if not is_valid_email(contact_address):
        LOG.w(
            "invalid reply-to address %s. Parse from %s",
            contact_address,
            reply_to_header,
        )
        return None

    contact = Contact.get_by(alias_id=alias.id, website_email=contact_address)
    if contact:
        return contact
    else:
        LOG.d(
            "create contact %s for alias %s via reply-to header",
            contact_address,
            alias,
            reply_to_header,
        )

        try:
            contact = Contact.create(
                user_id=alias.user_id,
                alias_id=alias.id,
                website_email=contact_address,
                name=contact_name,
                reply_email=generate_reply_email(contact_address, alias.user),
            )
            db.session.commit()
        except IntegrityError:
            LOG.w("Contact %s %s already exist", alias, contact_address)
            db.session.rollback()
            contact = Contact.get_by(alias_id=alias.id, website_email=contact_address)

    return contact


def replace_header_when_forward(msg: Message, alias: Alias, header: str):
    """
    Replace CC or To header by Reply emails in forward phase
    """
    new_addrs: [str] = []
    headers = msg.get_all(header, [])
    # headers can be an array of Header, convert it to string here
    headers = [get_header_unicode(h) for h in headers]

    full_addresses: [EmailAddress] = []
    for h in headers:
        full_addresses += address.parse_list(h)

    for full_address in full_addresses:
        contact_email = sanitize_email(full_address.address)

        # no transformation when alias is already in the header
        if contact_email == alias.email:
            new_addrs.append(full_address.full_spec())
            continue

        try:
            # NOT allow unicode for contact address
            validate_email(
                contact_email, check_deliverability=False, allow_smtputf8=False
            )
        except EmailNotValidError:
            LOG.w("invalid contact email %s. %s. Skip", contact_email, headers)
            continue

        contact = Contact.get_by(alias_id=alias.id, website_email=contact_email)
        if contact:
            # update the contact name if needed
            if contact.name != full_address.display_name:
                LOG.d(
                    "Update contact %s name %s to %s",
                    contact,
                    contact.name,
                    full_address.display_name,
                )
                contact.name = full_address.display_name
                db.session.commit()
        else:
            LOG.d(
                "create contact for alias %s and email %s, header %s",
                alias,
                contact_email,
                header,
            )

            try:
                contact = Contact.create(
                    user_id=alias.user_id,
                    alias_id=alias.id,
                    website_email=contact_email,
                    name=full_address.display_name,
                    reply_email=generate_reply_email(contact_email, alias.user),
                    is_cc=header.lower() == "cc",
                )
                db.session.commit()
            except IntegrityError:
                LOG.w("Contact %s %s already exist", alias, contact_email)
                db.session.rollback()
                contact = Contact.get_by(alias_id=alias.id, website_email=contact_email)

        new_addrs.append(contact.new_addr())

    if new_addrs:
        new_header = ",".join(new_addrs)
        LOG.d("Replace %s header, old: %s, new: %s", header, msg[header], new_header)
        add_or_replace_header(msg, header, new_header)
    else:
        LOG.d("Delete %s header, old value %s", header, msg[header])
        delete_header(msg, header)


def replace_header_when_reply(msg: Message, alias: Alias, header: str):
    """
    Replace CC or To Reply emails by original emails
    """
    new_addrs: [str] = []
    headers = msg.get_all(header, [])
    # headers can be an array of Header, convert it to string here
    headers = [str(h) for h in headers]

    for _, reply_email in getaddresses(headers):
        # no transformation when alias is already in the header
        if reply_email == alias.email:
            continue

        contact = Contact.get_by(reply_email=reply_email)
        if not contact:
            LOG.w(
                "%s email in reply phase %s must be reply emails", header, reply_email
            )
            # still keep this email in header
            new_addrs.append(reply_email)
        else:
            new_addrs.append(formataddr((contact.name, contact.website_email)))

    if new_addrs:
        new_header = ",".join(new_addrs)
        LOG.d("Replace %s header, old: %s, new: %s", header, msg[header], new_header)
        add_or_replace_header(msg, header, new_header)
    else:
        LOG.d("delete the %s header. Old value %s", header, msg[header])
        delete_header(msg, header)


def prepare_pgp_message(
    orig_msg: Message, pgp_fingerprint: str, public_key: str, can_sign: bool = False
) -> Message:
    msg = MIMEMultipart("encrypted", protocol="application/pgp-encrypted")

    # clone orig message to avoid modifying it
    clone_msg = copy(orig_msg)

    # copy all headers from original message except all standard MIME headers
    for i in reversed(range(len(clone_msg._headers))):
        header_name = clone_msg._headers[i][0].lower()
        if header_name.lower() not in _MIME_HEADERS:
            msg[header_name] = clone_msg._headers[i][1]

    # Delete unnecessary headers in clone_msg except _MIME_HEADERS to save space
    delete_all_headers_except(
        clone_msg,
        _MIME_HEADERS,
    )

    if clone_msg["Content-Type"] is None:
        LOG.d("Content-Type missing")
        clone_msg["Content-Type"] = "text/plain"

    if clone_msg["Mime-Version"] is None:
        LOG.d("Mime-Version missing")
        clone_msg["Mime-Version"] = "1.0"

    first = MIMEApplication(
        _subtype="pgp-encrypted", _encoder=encoders.encode_7or8bit, _data=""
    )
    first.set_payload("Version: 1")
    msg.attach(first)

    if can_sign and PGP_SENDER_PRIVATE_KEY:
        LOG.d("Sign msg")
        clone_msg = sign_msg(clone_msg)

    # use pgpy as fallback
    second = MIMEApplication(
        "octet-stream", _encoder=encoders.encode_7or8bit, name="encrypted.asc"
    )
    second.add_header("Content-Disposition", 'inline; filename="encrypted.asc"')

    # encrypt
    # use pgpy as fallback
    msg_bytes = to_bytes(clone_msg)
    try:
        encrypted_data = pgp_utils.encrypt_file(BytesIO(msg_bytes), pgp_fingerprint)
        second.set_payload(encrypted_data)
    except PGPException:
        LOG.w("Cannot encrypt using python-gnupg, use pgpy")
        encrypted = pgp_utils.encrypt_file_with_pgpy(msg_bytes, public_key)
        second.set_payload(str(encrypted))

    msg.attach(second)

    return msg


def sign_msg(msg: Message) -> Message:
    container = MIMEMultipart(
        "signed", protocol="application/pgp-signature", micalg="pgp-sha256"
    )
    container.attach(msg)

    signature = MIMEApplication(
        _subtype="pgp-signature", name="signature.asc", _data="", _encoder=encode_noop
    )
    signature.add_header("Content-Disposition", 'attachment; filename="signature.asc"')

    try:
        signature.set_payload(sign_data(to_bytes(msg).replace(b"\n", b"\r\n")))
    except Exception:
        LOG.e("Cannot sign, try using pgpy")
        signature.set_payload(
            sign_data_with_pgpy(to_bytes(msg).replace(b"\n", b"\r\n"))
        )

    container.attach(signature)

    return container


def handle_email_sent_to_ourself(alias, mailbox, msg: Message, user):
    # store the refused email
    random_name = str(uuid.uuid4())
    full_report_path = f"refused-emails/cycle-{random_name}.eml"
    s3.upload_email_from_bytesio(full_report_path, BytesIO(to_bytes(msg)), random_name)
    refused_email = RefusedEmail.create(
        path=None, full_report_path=full_report_path, user_id=alias.user_id
    )
    db.session.commit()
    LOG.d("Create refused email %s", refused_email)
    # link available for 6 days as it gets deleted in 7 days
    refused_email_url = refused_email.get_url(expires_in=518400)

    send_email_at_most_times(
        user,
        ALERT_SEND_EMAIL_CYCLE,
        mailbox.email,
        f"Email sent to {alias.email} from its own mailbox {mailbox.email}",
        render(
            "transactional/cycle-email.txt",
            alias=alias,
            mailbox=mailbox,
            refused_email_url=refused_email_url,
        ),
        render(
            "transactional/cycle-email.html",
            alias=alias,
            mailbox=mailbox,
            refused_email_url=refused_email_url,
        ),
    )


def handle_forward(envelope, msg: Message, rcpt_to: str) -> List[Tuple[bool, str]]:
    """return an array of SMTP status (is_success, smtp_status)
    is_success indicates whether an email has been delivered and
    smtp_status is the SMTP Status ("250 Message accepted", "550 Non-existent email address", etc)
    """
    alias_address = rcpt_to  # alias@SL

    alias = Alias.get_by(email=alias_address)
    if not alias:
        LOG.d(
            "alias %s not exist. Try to see if it can be created on the fly",
            alias_address,
        )
        alias = try_auto_create(alias_address)
        if not alias:
            LOG.d("alias %s cannot be created on-the-fly, return 550", alias_address)
            if should_ignore_bounce(envelope.mail_from):
                return [(True, status.E207)]
            else:
                return [(False, status.E515)]

    user = alias.user

    if user.disabled:
        LOG.w("User %s disabled, disable forwarding emails for %s", user, alias)
        if should_ignore_bounce(envelope.mail_from):
            return [(True, status.E207)]
        else:
            return [(False, status.E504)]

    if user.ignore_loop_email:
        mail_from = envelope.mail_from
        for mb in alias.mailboxes:
            # email sent from a mailbox to its alias
            if mb.email == mail_from:
                LOG.w("cycle email sent from %s to %s", mb, alias)
                handle_email_sent_to_ourself(alias, mb, msg, user)
                return [(True, status.E209)]

    from_header = get_header_unicode(msg["From"])
    LOG.d("Create or get contact for from_header:%s", from_header)
    contact = get_or_create_contact(from_header, envelope.mail_from, alias)

    reply_to_contact = None
    if msg["Reply-To"]:
        reply_to = get_header_unicode(msg["Reply-To"])
        LOG.d("Create or get contact for from_header:%s", reply_to)
        # ignore when reply-to = alias
        if reply_to == alias.email:
            LOG.i("Reply-to same as alias %s", alias)
        else:
            reply_to_contact = get_or_create_reply_to_contact(reply_to, alias)

    if not alias.enabled:
        LOG.d("%s is disabled, do not forward", alias)
        EmailLog.create(
            contact_id=contact.id,
            user_id=contact.user_id,
            blocked=True,
            alias_id=contact.alias_id,
            commit=True,
        )
        db.session.commit()
        # do not return 5** to allow user to receive emails later when alias is enabled
        return [(True, status.E200)]

    ret = []
    mailboxes = alias.mailboxes

    # no valid mailbox
    if not mailboxes:
        if should_ignore_bounce(envelope.mail_from):
            return [(True, status.E207)]
        else:
            return [(False, status.E516)]

    # no need to create a copy of message
    for mailbox in mailboxes:
        if not mailbox.verified:
            LOG.d("%s unverified, do not forward", mailbox)
            ret.append((False, status.E517))
        else:
            # create a copy of message for each forward
            ret.append(
                forward_email_to_mailbox(
                    alias, copy(msg), contact, envelope, mailbox, user, reply_to_contact
                )
            )

    return ret


def forward_email_to_mailbox(
    alias,
    msg: Message,
    contact: Contact,
    envelope,
    mailbox,
    user,
    reply_to_contact: Optional[Contact],
) -> (bool, str):
    LOG.d("Forward %s -> %s -> %s", contact, alias, mailbox)

    if mailbox.disabled:
        LOG.d("%s disabled, do not forward")
        if should_ignore_bounce(envelope.mail_from):
            return True, status.E207
        else:
            return False, status.E518

    # sanity check: make sure mailbox is not actually an alias
    if get_email_domain_part(alias.email) == get_email_domain_part(mailbox.email):
        LOG.w(
            "Mailbox has the same domain as alias. %s -> %s -> %s",
            contact,
            alias,
            mailbox,
        )
        mailbox_url = f"{URL}/dashboard/mailbox/{mailbox.id}/"
        send_email_with_rate_control(
            user,
            ALERT_MAILBOX_IS_ALIAS,
            user.email,
            f"Your mailbox {mailbox.email} and alias {alias.email} use the same domain",
            render(
                "transactional/mailbox-invalid.txt",
                mailbox=mailbox,
                mailbox_url=mailbox_url,
                alias=alias,
            ),
            render(
                "transactional/mailbox-invalid.html",
                mailbox=mailbox,
                mailbox_url=mailbox_url,
                alias=alias,
            ),
            max_nb_alert=1,
        )

        # retry later
        # so when user fixes the mailbox, the email can be delivered
        return False, status.E405

    email_log = EmailLog.create(
        contact_id=contact.id,
        user_id=user.id,
        mailbox_id=mailbox.id,
        alias_id=contact.alias_id,
        commit=True,
    )
    LOG.d("Create %s for %s, %s, %s", email_log, contact, user, mailbox)

    if ENABLE_SPAM_ASSASSIN:
        # Spam check
        spam_status = ""
        is_spam = False

        if SPAMASSASSIN_HOST:
            start = time.time()
            spam_score, spam_report = get_spam_score(msg, email_log)
            LOG.d(
                "%s -> %s - spam score:%s in %s seconds. Spam report %s",
                contact,
                alias,
                spam_score,
                time.time() - start,
                spam_report,
            )
            email_log.spam_score = spam_score
            db.session.commit()

            if (user.max_spam_score and spam_score > user.max_spam_score) or (
                not user.max_spam_score and spam_score > MAX_SPAM_SCORE
            ):
                is_spam = True
                # only set the spam report for spam
                email_log.spam_report = spam_report
        else:
            is_spam, spam_status = get_spam_info(msg, max_score=user.max_spam_score)

        if is_spam:
            LOG.w(
                "Email detected as spam. %s -> %s. Spam Score: %s, Spam Report: %s",
                contact,
                alias,
                email_log.spam_score,
                email_log.spam_report,
            )
            email_log.is_spam = True
            email_log.spam_status = spam_status
            db.session.commit()

            handle_spam(contact, alias, msg, user, mailbox, email_log)
            return False, status.E519

    if contact.invalid_email:
        LOG.d("add noreply information %s %s", alias, mailbox)
        msg = add_header(
            msg,
            f"""Email sent to {alias.email} from an invalid address and cannot be replied""",
            f"""Email sent to {alias.email} from an invalid address and cannot be replied""",
        )

    delete_all_headers_except(
        msg,
        [
            "From",
            "To",
            "Cc",
            "Subject",
            # References and In-Reply-To are used for keeping the email thread
            "References",
            "In-Reply-To",
        ]
        + _MIME_HEADERS,
    )

    # create PGP email if needed
    if mailbox.pgp_enabled() and user.is_premium() and not alias.disable_pgp:
        LOG.d("Encrypt message using mailbox %s", mailbox)
        if mailbox.generic_subject:
            LOG.d("Use a generic subject for %s", mailbox)
            orig_subject = msg["Subject"]
            orig_subject = get_header_unicode(orig_subject)
            add_or_replace_header(msg, "Subject", mailbox.generic_subject)
            msg = add_header(
                msg,
                f"""Forwarded by SimpleLogin to {alias.email} with "{orig_subject}" as subject""",
                f"""Forwarded by SimpleLogin to {alias.email} with <b>{orig_subject}</b> as subject""",
            )

        try:
            msg = prepare_pgp_message(
                msg, mailbox.pgp_finger_print, mailbox.pgp_public_key, can_sign=True
            )
        except PGPException:
            LOG.e(
                "Cannot encrypt message %s -> %s. %s %s", contact, alias, mailbox, user
            )
            # so the client can retry later
            return False, status.E406

    # add custom header
    add_or_replace_header(msg, _DIRECTION, "Forward")

    msg[_EMAIL_LOG_ID_HEADER] = str(email_log.id)
    msg[_ENVELOPE_FROM] = envelope.mail_from
    # when an alias isn't in the To: header, there's no way for users to know what alias has received the email
    msg[_ENVELOPE_TO] = alias.email
    message_id = make_msgid(str(email_log.id), EMAIL_DOMAIN)
    LOG.d("message id %s", message_id)
    msg["Message-ID"] = message_id
    msg["Date"] = formatdate()

    # change the from header so the sender comes from a reverse-alias
    # so it can pass DMARC check
    # replace the email part in from: header
    contact_from_header = msg["From"]
    new_from_header = contact.new_addr()
    add_or_replace_header(msg, "From", new_from_header)
    LOG.d("From header, new:%s, old:%s", new_from_header, contact_from_header)

    if reply_to_contact:
        reply_to_header = msg["Reply-To"]
        new_reply_to_header = reply_to_contact.new_addr()
        add_or_replace_header(msg, "Reply-To", new_reply_to_header)
        LOG.d("Reply-To header, new:%s, old:%s", new_reply_to_header, reply_to_header)

    # replace CC & To emails by reverse-alias for all emails that are not alias
    replace_header_when_forward(msg, alias, "Cc")
    replace_header_when_forward(msg, alias, "To")

    # add List-Unsubscribe header
    unsubscribe_link, via_email = alias.unsubscribe_link()
    add_or_replace_header(msg, "List-Unsubscribe", f"<{unsubscribe_link}>")
    if not via_email:
        add_or_replace_header(
            msg, "List-Unsubscribe-Post", "List-Unsubscribe=One-Click"
        )

    add_dkim_signature(msg, EMAIL_DOMAIN)

    LOG.d(
        "Forward mail from %s to %s, mail_options:%s, rcpt_options:%s ",
        contact.website_email,
        mailbox.email,
        envelope.mail_options,
        envelope.rcpt_options,
    )

    try:
        sl_sendmail(
            # use a different envelope sender for each forward (aka VERP)
            BOUNCE_EMAIL.format(email_log.id),
            mailbox.email,
            msg,
            envelope.mail_options,
            envelope.rcpt_options,
            is_forward=True,
        )
    except SMTPRecipientsRefused:
        # that means the mailbox is maybe invalid
        LOG.w(
            "SMTPRecipientsRefused forward phase %s -> %s -> %s",
            contact,
            alias,
            mailbox,
        )
        if should_ignore_bounce(envelope.mail_from):
            return True, status.E207
        else:
            return False, status.E521
    else:
        db.session.commit()
        return True, status.E200


def handle_reply(envelope, msg: Message, rcpt_to: str) -> (bool, str):
    """
    Return whether an email has been delivered and
    the smtp status ("250 Message accepted", "550 Non-existent email address", etc)
    """
    reply_email = rcpt_to

    # reply_email must end with EMAIL_DOMAIN
    if not reply_email.endswith(EMAIL_DOMAIN):
        LOG.w(f"Reply email {reply_email} has wrong domain")
        return False, status.E501

    # handle case where reply email is generated with non-allowed char
    reply_email = normalize_reply_email(reply_email)

    contact = Contact.get_by(reply_email=reply_email)
    if not contact:
        LOG.w(f"No such forward-email with {reply_email} as reply-email")
        return False, status.E502

    alias = contact.alias
    address: str = contact.alias.email
    alias_domain = address[address.find("@") + 1 :]

    # Sanity check: verify alias domain is managed by SimpleLogin
    # scenario: a user have removed a domain but due to a bug, the aliases are still there
    if not is_valid_alias_address_domain(alias.email):
        LOG.e("%s domain isn't known", alias)
        return False, status.E503

    user = alias.user
    mail_from = envelope.mail_from

    if user.disabled:
        LOG.e(
            "User %s disabled, disable sending emails from %s to %s",
            user,
            alias,
            contact,
        )
        return [(False, status.E504)]

    # Anti-spoofing
    mailbox = get_mailbox_from_mail_from(mail_from, alias)
    if not mailbox:
        if alias.disable_email_spoofing_check:
            # ignore this error, use default alias mailbox
            LOG.w(
                "ignore unknown sender to reverse-alias %s: %s -> %s",
                mail_from,
                alias,
                contact,
            )
            mailbox = alias.mailbox
        else:
            # only mailbox can send email to the reply-email
            handle_unknown_mailbox(envelope, msg, reply_email, user, alias, contact)
            return False, status.E505

    if ENFORCE_SPF and mailbox.force_spf and not alias.disable_email_spoofing_check:
        if not spf_pass(envelope, mailbox, user, alias, contact.website_email, msg):
            # cannot use 4** here as sender will retry.
            # cannot use 5** because that generates bounce report
            return True, status.E201

    email_log = EmailLog.create(
        contact_id=contact.id,
        alias_id=contact.alias_id,
        is_reply=True,
        user_id=contact.user_id,
        mailbox_id=mailbox.id,
        commit=True,
    )
    LOG.d("Create %s for %s, %s, %s", email_log, contact, user, mailbox)

    # Spam check
    if ENABLE_SPAM_ASSASSIN:
        spam_status = ""
        is_spam = False

        # do not use user.max_spam_score here
        if SPAMASSASSIN_HOST:
            start = time.time()
            spam_score, spam_report = get_spam_score(msg, email_log)
            LOG.d(
                "%s -> %s - spam score %s in %s seconds. Spam report %s",
                alias,
                contact,
                spam_score,
                time.time() - start,
                spam_report,
            )
            email_log.spam_score = spam_score
            if spam_score > MAX_REPLY_PHASE_SPAM_SCORE:
                is_spam = True
                # only set the spam report for spam
                email_log.spam_report = spam_report
        else:
            is_spam, spam_status = get_spam_info(
                msg, max_score=MAX_REPLY_PHASE_SPAM_SCORE
            )

        if is_spam:
            LOG.w(
                "Email detected as spam. Reply phase. %s -> %s. Spam Score: %s, Spam Report: %s",
                alias,
                contact,
                email_log.spam_score,
                email_log.spam_report,
            )

            email_log.is_spam = True
            email_log.spam_status = spam_status
            db.session.commit()

            handle_spam(contact, alias, msg, user, mailbox, email_log, is_reply=True)
            return False, status.E506

    delete_all_headers_except(
        msg,
        [
            "From",
            "To",
            "Cc",
            "Subject",
            # References and In-Reply-To are used for keeping the email thread
            "References",
            "In-Reply-To",
        ]
        + _MIME_HEADERS,
    )

    # replace the reverse-alias (i.e. "ra+string@simplelogin.co") by the contact email in the email body
    # as this is usually included when replying
    if user.replace_reverse_alias:
        LOG.d("Replace reverse-alias %s by contact email %s", reply_email, contact)
        msg = replace(msg, reply_email, contact.website_email)

    # create PGP email if needed
    if contact.pgp_finger_print and user.is_premium():
        LOG.d("Encrypt message for contact %s", contact)
        try:
            msg = prepare_pgp_message(
                msg, contact.pgp_finger_print, contact.pgp_public_key
            )
        except PGPException:
            LOG.e(
                "Cannot encrypt message %s -> %s. %s %s", alias, contact, mailbox, user
            )
            # to not save the email_log
            EmailLog.delete(email_log.id)
            db.session.commit()
            # return 421 so the client can retry later
            return False, status.E402

    db.session.commit()

    # make the email comes from alias
    from_header = alias.email
    # add alias name from alias
    if alias.name:
        LOG.d("Put alias name in from header")
        from_header = formataddr((alias.name, alias.email))
    elif alias.custom_domain:
        LOG.d("Put domain default alias name in from header")

        # add alias name from domain
        if alias.custom_domain.name:
            from_header = formataddr((alias.custom_domain.name, alias.email))

    add_or_replace_header(msg, "From", from_header)

    replace_header_when_reply(msg, alias, "To")
    replace_header_when_reply(msg, alias, "Cc")

    # Message-ID can reveal about the mailbox -> replace it
    message_id = make_msgid(str(email_log.id), get_email_domain_part(alias.email))
    LOG.d("make message id %s", message_id)
    add_or_replace_header(
        msg,
        "Message-ID",
        message_id,
    )
    date_header = formatdate()
    msg["Date"] = date_header

    msg[_DIRECTION] = "Reply"
    msg[_EMAIL_LOG_ID_HEADER] = str(email_log.id)

    LOG.d(
        "send email from %s to %s, mail_options:%s,rcpt_options:%s",
        alias.email,
        contact.website_email,
        envelope.mail_options,
        envelope.rcpt_options,
    )

    if should_add_dkim_signature(alias_domain):
        add_dkim_signature(msg, alias_domain)

    # generate a mail_from for VERP
    verp_mail_from = f"{BOUNCE_PREFIX_FOR_REPLY_PHASE}+{email_log.id}+@{alias_domain}"

    try:
        sl_sendmail(
            verp_mail_from,
            contact.website_email,
            msg,
            envelope.mail_options,
            envelope.rcpt_options,
            is_forward=False,
        )
    except Exception:
        # to not save the email_log
        db.session.rollback()

        LOG.w("Cannot send email from %s to %s", alias, contact)
        send_email(
            mailbox.email,
            f"Email cannot be sent to {contact.email} from {alias.email}",
            render(
                "transactional/reply-error.txt",
                user=user,
                alias=alias,
                contact=contact,
                contact_domain=get_email_domain_part(contact.email),
            ),
            render(
                "transactional/reply-error.html",
                user=user,
                alias=alias,
                contact=contact,
                contact_domain=get_email_domain_part(contact.email),
            ),
        )

    # return 250 even if error as user is already informed of the incident and can retry sending the email
    return True, status.E200


def get_mailbox_from_mail_from(mail_from: str, alias) -> Optional[Mailbox]:
    """return the corresponding mailbox given the mail_from and alias
    Usually the mail_from=mailbox.email but it can also be one of the authorized address
    """
    for mailbox in alias.mailboxes:
        if mailbox.email == mail_from:
            return mailbox

        for addr in mailbox.authorized_addresses:
            if addr.email == mail_from:
                LOG.d(
                    "Found an authorized address for %s %s %s", alias, mailbox, address
                )
                return mailbox

    return None


def handle_unknown_mailbox(
    envelope, msg, reply_email: str, user: User, alias: Alias, contact: Contact
):
    LOG.w(
        "Reply email can only be used by mailbox. "
        "Actual mail_from: %s. msg from header: %s, reverse-alias %s, %s %s %s",
        envelope.mail_from,
        msg["From"],
        reply_email,
        alias,
        user,
        contact,
    )

    authorize_address_link = (
        f"{URL}/dashboard/mailbox/{alias.mailbox_id}/#authorized-address"
    )
    mailbox_emails = [mailbox.email for mailbox in alias.mailboxes]
    send_email_with_rate_control(
        user,
        ALERT_REVERSE_ALIAS_UNKNOWN_MAILBOX,
        user.email,
        f"Attempt to use your alias {alias.email} from {envelope.mail_from}",
        render(
            "transactional/reply-must-use-personal-email.txt",
            alias=alias,
            sender=envelope.mail_from,
            authorize_address_link=authorize_address_link,
            mailbox_emails=mailbox_emails,
        ),
        render(
            "transactional/reply-must-use-personal-email.html",
            alias=alias,
            sender=envelope.mail_from,
            authorize_address_link=authorize_address_link,
            mailbox_emails=mailbox_emails,
        ),
    )

    # Notify sender that they cannot send emails to this address
    send_email_with_rate_control(
        user,
        ALERT_REVERSE_ALIAS_UNKNOWN_MAILBOX,
        envelope.mail_from,
        f"Your email ({envelope.mail_from}) is not allowed to send emails to {reply_email}",
        render(
            "transactional/send-from-alias-from-unknown-sender.txt",
            sender=envelope.mail_from,
            reply_email=reply_email,
        ),
        render(
            "transactional/send-from-alias-from-unknown-sender.html",
            sender=envelope.mail_from,
            reply_email=reply_email,
        ),
    )


def handle_bounce_forward_phase(msg: Message, email_log: EmailLog):
    """
    Handle forward phase bounce
    Happens when an email cannot be sent to a mailbox
    """
    contact = email_log.contact
    alias = contact.alias
    user = alias.user
    mailbox = email_log.mailbox

    # email_log.mailbox should be set during the forward phase
    if not mailbox:
        LOG.e("Use %s default mailbox %s", alias, alias.mailbox)
        mailbox = alias.mailbox

    Bounce.create(email=mailbox.email, commit=True)

    LOG.d(
        "Handle forward bounce %s -> %s -> %s. %s", contact, alias, mailbox, email_log
    )

    # Store the bounced email, generate a name for the email
    random_name = str(uuid.uuid4())

    full_report_path = f"refused-emails/full-{random_name}.eml"
    s3.upload_email_from_bytesio(
        full_report_path, BytesIO(to_bytes(msg)), f"full-{random_name}"
    )

    file_path = None

    orig_msg = get_orig_message_from_bounce(msg)
    if not orig_msg:
        # Some MTA does not return the original message in bounce message
        # nothing we can do here
        LOG.w(
            "Cannot parse original message from bounce message %s %s %s %s",
            alias,
            user,
            contact,
            full_report_path,
        )
    else:
        file_path = f"refused-emails/{random_name}.eml"
        s3.upload_email_from_bytesio(
            file_path, BytesIO(to_bytes(orig_msg)), random_name
        )

    refused_email = RefusedEmail.create(
        path=file_path, full_report_path=full_report_path, user_id=user.id
    )
    db.session.flush()
    LOG.d("Create refused email %s", refused_email)

    email_log.bounced = True
    email_log.refused_email_id = refused_email.id
    email_log.bounced_mailbox_id = mailbox.id
    db.session.commit()

    refused_email_url = f"{URL}/dashboard/refused_email?highlight_id={email_log.id}"

    # inform user of this bounce
    if not should_disable(alias):
        LOG.d(
            "Inform user %s about a bounce from contact %s to alias %s",
            user,
            contact,
            alias,
        )
        disable_alias_link = f"{URL}/dashboard/unsubscribe/{alias.id}"
        send_email_with_rate_control(
            user,
            ALERT_BOUNCE_EMAIL,
            user.email,
            f"Email from {contact.website_email} to {alias.email} cannot be delivered to your mailbox",
            render(
                "transactional/bounce/bounced-email.txt",
                alias=alias,
                website_email=contact.website_email,
                disable_alias_link=disable_alias_link,
                refused_email_url=refused_email_url,
                mailbox_email=mailbox.email,
            ),
            render(
                "transactional/bounce/bounced-email.html",
                alias=alias,
                website_email=contact.website_email,
                disable_alias_link=disable_alias_link,
                refused_email_url=refused_email_url,
                mailbox_email=mailbox.email,
            ),
            max_nb_alert=10,
            # smtp error can happen if user mailbox is unreachable, that might explain the bounce
            ignore_smtp_error=True,
        )
    else:
        LOG.w(
            "Disable alias %s now",
            alias,
        )
        alias.enabled = False
        db.session.commit()

        send_email_with_rate_control(
            user,
            ALERT_BOUNCE_EMAIL,
            user.email,
            f"Alias {alias.email} has been disabled due to multiple bounces",
            render(
                "transactional/bounce/automatic-disable-alias.txt",
                alias=alias,
                refused_email_url=refused_email_url,
                mailbox_email=mailbox.email,
            ),
            render(
                "transactional/bounce/automatic-disable-alias.html",
                alias=alias,
                refused_email_url=refused_email_url,
                mailbox_email=mailbox.email,
            ),
            max_nb_alert=10,
            ignore_smtp_error=True,
        )


def handle_hotmail_complaint(msg: Message) -> bool:
    """
    Handle hotmail complaint sent to postmaster
    Return True if the complaint can be handled, False otherwise
    """
    orig_msg = get_orig_message_from_hotmail_complaint(msg)
    to_header = orig_msg["To"]
    if not to_header:
        LOG.e("cannot find the alias")
        return False

    _, alias_address = parse_full_address(get_header_unicode(to_header))
    alias = Alias.get_by(email=alias_address)

    if not alias:
        LOG.w("No alias for %s", alias_address)
        return False

    user = alias.user
    LOG.w("Handle hotmail complaint for %s %s %s", alias, user, alias.mailboxes)

    send_email_with_rate_control(
        user,
        ALERT_HOTMAIL_COMPLAINT,
        user.email,
        f"Hotmail abuse report",
        render(
            "transactional/hotmail-complaint.txt.jinja2",
            alias=alias,
        ),
        render(
            "transactional/hotmail-complaint.html",
            alias=alias,
        ),
        max_nb_alert=2,
    )

    return True


def handle_yahoo_complaint(msg: Message) -> bool:
    """
    Handle yahoo complaint sent to postmaster
    Return True if the complaint can be handled, False otherwise
    """
    orig_msg = get_orig_message_from_yahoo_complaint(msg)
    to_header = orig_msg["To"]
    if not to_header:
        LOG.e("cannot find the alias")
        return False

    _, alias_address = parse_full_address(get_header_unicode(to_header))
    alias = Alias.get_by(email=alias_address)

    if not alias:
        LOG.w("No alias for %s", alias_address)
        return False

    user = alias.user
    LOG.w("Handle yahoo complaint for %s %s %s", alias, user, alias.mailboxes)

    send_email_with_rate_control(
        user,
        ALERT_YAHOO_COMPLAINT,
        user.email,
        f"Yahoo abuse report",
        render(
            "transactional/yahoo-complaint.txt.jinja2",
            alias=alias,
        ),
        render(
            "transactional/yahoo-complaint.html",
            alias=alias,
        ),
        max_nb_alert=2,
    )

    return True


def handle_bounce_reply_phase(envelope, msg: Message, email_log: EmailLog):
    """
    Handle reply phase bounce
    Happens when  an email cannot be sent from an alias to a contact
    """
    contact: Contact = email_log.contact
    alias = contact.alias
    user = alias.user
    mailbox = email_log.mailbox or alias.mailbox

    LOG.d("Handle reply bounce %s -> %s -> %s.%s", mailbox, alias, contact, email_log)

    Bounce.create(email=sanitize_email(contact.website_email), commit=True)

    # Store the bounced email
    # generate a name for the email
    random_name = str(uuid.uuid4())

    full_report_path = f"refused-emails/full-{random_name}.eml"
    s3.upload_email_from_bytesio(full_report_path, BytesIO(to_bytes(msg)), random_name)

    orig_msg = get_orig_message_from_bounce(msg)
    file_path = None
    if orig_msg:
        file_path = f"refused-emails/{random_name}.eml"
        s3.upload_email_from_bytesio(
            file_path, BytesIO(to_bytes(orig_msg)), random_name
        )

    refused_email = RefusedEmail.create(
        path=file_path, full_report_path=full_report_path, user_id=user.id, commit=True
    )
    LOG.d("Create refused email %s", refused_email)

    email_log.bounced = True
    email_log.refused_email_id = refused_email.id

    email_log.bounced_mailbox_id = mailbox.id

    db.session.commit()

    refused_email_url = f"{URL}/dashboard/refused_email?highlight_id={email_log.id}"

    LOG.d(
        "Inform user %s about bounced email sent by %s to %s",
        user,
        alias,
        contact,
    )
    send_email_with_rate_control(
        user,
        ALERT_BOUNCE_EMAIL_REPLY_PHASE,
        mailbox.email,
        f"Email cannot be sent to { contact.email } from your alias { alias.email }",
        render(
            "transactional/bounce/bounce-email-reply-phase.txt",
            alias=alias,
            contact=contact,
            refused_email_url=refused_email_url,
        ),
        render(
            "transactional/bounce/bounce-email-reply-phase.html",
            alias=alias,
            contact=contact,
            refused_email_url=refused_email_url,
        ),
    )
    return status.E520


def handle_spam(
    contact: Contact,
    alias: Alias,
    msg: Message,
    user: User,
    mailbox: Mailbox,
    email_log: EmailLog,
    is_reply=False,  # whether the email is in forward or reply phase
):
    # Store the report & original email
    orig_msg = get_orig_message_from_spamassassin_report(msg)
    # generate a name for the email
    random_name = str(uuid.uuid4())

    full_report_path = f"spams/full-{random_name}.eml"
    s3.upload_email_from_bytesio(full_report_path, BytesIO(to_bytes(msg)), random_name)

    file_path = None
    if orig_msg:
        file_path = f"spams/{random_name}.eml"
        s3.upload_email_from_bytesio(
            file_path, BytesIO(to_bytes(orig_msg)), random_name
        )

    refused_email = RefusedEmail.create(
        path=file_path, full_report_path=full_report_path, user_id=user.id
    )
    db.session.flush()

    email_log.refused_email_id = refused_email.id
    db.session.commit()

    LOG.d("Create spam email %s", refused_email)

    refused_email_url = f"{URL}/dashboard/refused_email?highlight_id={email_log.id}"
    disable_alias_link = f"{URL}/dashboard/unsubscribe/{alias.id}"

    if is_reply:
        LOG.d(
            "Inform %s (%s) about spam email sent from alias %s to %s. %s",
            mailbox,
            user,
            alias,
            contact,
            refused_email,
        )
        send_email_with_rate_control(
            user,
            ALERT_SPAM_EMAIL,
            mailbox.email,
            f"Email from {alias.email} to {contact.website_email} is detected as spam",
            render(
                "transactional/spam-email-reply-phase.txt",
                alias=alias,
                website_email=contact.website_email,
                disable_alias_link=disable_alias_link,
                refused_email_url=refused_email_url,
            ),
            render(
                "transactional/spam-email-reply-phase.html",
                alias=alias,
                website_email=contact.website_email,
                disable_alias_link=disable_alias_link,
                refused_email_url=refused_email_url,
            ),
        )
    else:
        # inform user
        LOG.d(
            "Inform %s (%s) about spam email sent by %s to alias %s",
            mailbox,
            user,
            contact,
            alias,
        )
        send_email_with_rate_control(
            user,
            ALERT_SPAM_EMAIL,
            mailbox.email,
            f"Email from {contact.website_email} to {alias.email} is detected as spam",
            render(
                "transactional/spam-email.txt",
                alias=alias,
                website_email=contact.website_email,
                disable_alias_link=disable_alias_link,
                refused_email_url=refused_email_url,
            ),
            render(
                "transactional/spam-email.html",
                alias=alias,
                website_email=contact.website_email,
                disable_alias_link=disable_alias_link,
                refused_email_url=refused_email_url,
            ),
        )


def handle_unsubscribe(envelope: Envelope, msg: Message) -> str:
    """return the SMTP status"""
    # format: alias_id:
    subject = msg["Subject"]
    try:
        # subject has the format {alias.id}=
        if subject.endswith("="):
            alias_id = int(subject[:-1])
        # {user.id}*
        elif subject.endswith("*"):
            user_id = int(subject[:-1])
            return handle_unsubscribe_user(user_id, envelope.mail_from)
        # some email providers might strip off the = suffix
        else:
            alias_id = int(subject)

        alias = Alias.get(alias_id)
    except Exception:
        LOG.w("Cannot parse alias from subject %s", msg["Subject"])
        return status.E507

    if not alias:
        LOG.w("No such alias %s", alias_id)
        return status.E508

    # This sender cannot unsubscribe
    mail_from = envelope.mail_from
    # Only alias's owning mailbox can send the unsubscribe request
    mailbox = get_mailbox_from_mail_from(mail_from, alias)
    if not mailbox:
        LOG.d("%s cannot disable alias %s", envelope.mail_from, alias)
        return status.E509

    # Sender is owner of this alias
    alias.enabled = False
    db.session.commit()
    user = alias.user

    enable_alias_url = URL + f"/dashboard/?highlight_alias_id={alias.id}"
    for mailbox in alias.mailboxes:
        send_email(
            mailbox.email,
            f"Alias {alias.email} has been disabled successfully",
            render(
                "transactional/unsubscribe-disable-alias.txt",
                user=user,
                alias=alias.email,
                enable_alias_url=enable_alias_url,
            ),
            render(
                "transactional/unsubscribe-disable-alias.html",
                user=user,
                alias=alias.email,
                enable_alias_url=enable_alias_url,
            ),
        )

    return status.E202


def handle_unsubscribe_user(user_id: int, mail_from: str) -> str:
    """return the SMTP status"""
    user = User.get(user_id)
    if not user:
        LOG.w("No such user %s %s", user_id, mail_from)
        return status.E510

    if mail_from != user.email:
        LOG.e("Unauthorized mail_from %s %s", user, mail_from)
        return status.E511

    user.notification = False
    db.session.commit()

    send_email(
        user.email,
        "You have been unsubscribed from SimpleLogin newsletter",
        render(
            "transactional/unsubscribe-newsletter.txt",
            user=user,
        ),
        render(
            "transactional/unsubscribe-newsletter.html",
            user=user,
        ),
    )

    return status.E202


def handle_transactional_bounce(envelope: Envelope, rcpt_to):
    LOG.d("handle transactional bounce sent to %s", rcpt_to)

    # parse the TransactionalEmail
    transactional_id = parse_id_from_bounce(rcpt_to)
    transactional = TransactionalEmail.get(transactional_id)

    # a transaction might have been deleted in delete_logs()
    if transactional:
        LOG.i("Create bounce for %s", transactional.email)
        Bounce.create(email=transactional.email, commit=True)


def handle_bounce(envelope, email_log: EmailLog, msg: Message) -> str:
    """
    Return SMTP status, e.g. "500 Error"
    """

    if not email_log:
        LOG.w("No such email log")
        return status.E512

    contact: Contact = email_log.contact
    alias = contact.alias
    LOG.d(
        "handle bounce for %s, phase=%s, contact=%s, alias=%s",
        email_log,
        email_log.get_phase(),
        contact,
        alias,
    )

    if email_log.is_reply:
        content_type = msg.get_content_type().lower()

        if content_type != "multipart/report" or envelope.mail_from != "<>":
            # forward the email again to the alias
            LOG.i(
                "Handle auto reply %s %s",
                content_type,
                envelope.mail_from,
            )

            contact: Contact = email_log.contact
            alias = contact.alias

            email_log.auto_replied = True
            db.session.commit()

            # replace the BOUNCE_EMAIL by alias in To field
            add_or_replace_header(msg, "To", alias.email)
            envelope.rcpt_tos = [alias.email]

            # same as handle()
            # result of all deliveries
            # each element is a couple of whether the delivery is successful and the smtp status
            res: [(bool, str)] = []

            for is_delivered, smtp_status in handle_forward(envelope, msg, alias.email):
                res.append((is_delivered, smtp_status))

            for (is_success, smtp_status) in res:
                # Consider all deliveries successful if 1 delivery is successful
                if is_success:
                    return smtp_status

            # Failed delivery for all, return the first failure
            return res[0][1]

        return handle_bounce_reply_phase(envelope, msg, email_log)
    else:  # forward phase
        handle_bounce_forward_phase(msg, email_log)
        return status.E513


def should_ignore(mail_from: str, rcpt_tos: List[str]) -> bool:
    if len(rcpt_tos) != 1:
        return False

    rcpt_to = rcpt_tos[0]
    if IgnoredEmail.get_by(mail_from=mail_from, rcpt_to=rcpt_to):
        return True

    return False


def handle(envelope: Envelope) -> str:
    """Return SMTP status"""

    # sanitize mail_from, rcpt_tos
    mail_from = sanitize_email(envelope.mail_from)
    rcpt_tos = [sanitize_email(rcpt_to) for rcpt_to in envelope.rcpt_tos]
    envelope.mail_from = mail_from
    envelope.rcpt_tos = rcpt_tos

    msg = email.message_from_bytes(envelope.original_content)
    postfix_queue_id = get_queue_id(msg)
    if postfix_queue_id:
        set_message_id(postfix_queue_id)
    else:
        LOG.d("Cannot parse Postfix queue ID from %s", msg["Received"])

    if should_ignore(mail_from, rcpt_tos):
        LOG.w("Ignore email mail_from=%s rcpt_to=%s", mail_from, rcpt_tos)
        return status.E204

    # sanitize email headers
    sanitize_header(msg, "from")
    sanitize_header(msg, "to")
    sanitize_header(msg, "cc")
    sanitize_header(msg, "reply-to")

    LOG.d(
        "==>> Handle mail_from:%s, rcpt_tos:%s, header_from:%s, header_to:%s, "
        "cc:%s, reply-to:%s, mail_options:%s, rcpt_options:%s",
        mail_from,
        rcpt_tos,
        msg["From"],
        msg["To"],
        msg["Cc"],
        msg["Reply-To"],
        envelope.mail_options,
        envelope.rcpt_options,
    )

    contact = Contact.get_by(reply_email=mail_from)
    if contact:
        LOG.w(
            "email can't be sent from a reverse-alias:%s, contact email:%s, %s, %s",
            contact.reply_email,
            contact.website_email,
            contact.alias,
            contact.user,
        )
        return status.E203

    # unsubscribe request
    if UNSUBSCRIBER and rcpt_tos == [UNSUBSCRIBER]:
        LOG.d("Handle unsubscribe request from %s", mail_from)
        return handle_unsubscribe(envelope, msg)

    # emails sent to sender. Probably bounce emails
    if (
        len(rcpt_tos) == 1
        and rcpt_tos[0].startswith(TRANSACTIONAL_BOUNCE_PREFIX)
        and rcpt_tos[0].endswith(TRANSACTIONAL_BOUNCE_SUFFIX)
    ):
        LOG.d("Handle email sent to sender from %s", mail_from)
        handle_transactional_bounce(envelope, rcpt_tos[0])
        return status.E205

    if (
        len(rcpt_tos) == 1
        and mail_from == "staff@hotmail.com"
        and rcpt_tos[0] == POSTMASTER
    ):
        LOG.w("Handle hotmail complaint")

        # if the complaint cannot be handled, forward it normally
        if handle_hotmail_complaint(msg):
            return status.E208

    if (
        len(rcpt_tos) == 1
        and mail_from == "feedback@arf.mail.yahoo.com"
        and rcpt_tos[0] == POSTMASTER
    ):
        LOG.w("Handle yahoo complaint")

        # if the complaint cannot be handled, forward it normally
        if handle_yahoo_complaint(msg):
            return status.E210

    # Handle bounce
    if (
        len(rcpt_tos) == 1
        and rcpt_tos[0].startswith(BOUNCE_PREFIX)
        and rcpt_tos[0].endswith(BOUNCE_SUFFIX)
    ):
        email_log_id = parse_id_from_bounce(rcpt_tos[0])
        email_log = EmailLog.get(email_log_id)
        return handle_bounce(envelope, email_log, msg)

    if len(rcpt_tos) == 1 and rcpt_tos[0].startswith(
        f"{BOUNCE_PREFIX_FOR_REPLY_PHASE}+"
    ):
        email_log_id = parse_id_from_bounce(rcpt_tos[0])
        email_log = EmailLog.get(email_log_id)
        return handle_bounce(envelope, email_log, msg)

    # iCloud returns the bounce with mail_from=bounce+{email_log_id}+@simplelogin.co, rcpt_to=alias
    if (
        len(rcpt_tos) == 1
        and mail_from.startswith(BOUNCE_PREFIX)
        and mail_from.endswith(BOUNCE_SUFFIX)
    ):
        email_log_id = parse_id_from_bounce(mail_from)
        email_log = EmailLog.get(email_log_id)
        alias = Alias.get_by(email=rcpt_tos[0])
        LOG.w(
            "iCloud bounces %s %s msg=%s",
            email_log,
            alias,
            msg.as_string(),
        )
        return handle_bounce(envelope, email_log, msg)

    if rate_limited(mail_from, rcpt_tos):
        LOG.w("Rate Limiting applied for mail_from:%s rcpt_tos:%s", mail_from, rcpt_tos)

        # add more logging info. TODO: remove
        if len(rcpt_tos) == 1:
            alias = Alias.get_by(email=rcpt_tos[0])
            if alias:
                LOG.w(
                    "total number email log on %s is %s",
                    alias,
                    EmailLog.query.filter(EmailLog.alias_id == alias.id).count(),
                )

        if should_ignore_bounce(envelope.mail_from):
            return status.E207
        else:
            return status.E522

    # Handle "out of office" auto notice. An automatic response is sent for every forwarded email
    # todo: remove logging
    if len(rcpt_tos) == 1 and is_reply_email(rcpt_tos[0]) and mail_from == "<>":
        LOG.w(
            "out-of-office email to reverse alias %s. %s", rcpt_tos[0], msg.as_string()
        )
        return status.E206

    # result of all deliveries
    # each element is a couple of whether the delivery is successful and the smtp status
    res: [(bool, str)] = []

    nb_rcpt_tos = len(rcpt_tos)
    for rcpt_index, rcpt_to in enumerate(rcpt_tos):
        if rcpt_to == NOREPLY:
            LOG.e("email sent to noreply address from %s", mail_from)
            return status.E514

        # create a copy of msg for each recipient except the last one
        # as copy() is a slow function
        if rcpt_index < nb_rcpt_tos - 1:
            LOG.d("copy message for rcpt %s", rcpt_to)
            copy_msg = copy(msg)
        else:
            copy_msg = msg

        # Reply case
        # recipient starts with "reply+" or "ra+" (ra=reverse-alias) prefix
        if is_reply_email(rcpt_to):
            LOG.d("Reply phase %s(%s) -> %s", mail_from, copy_msg["From"], rcpt_to)
            is_delivered, smtp_status = handle_reply(envelope, copy_msg, rcpt_to)
            res.append((is_delivered, smtp_status))
        else:  # Forward case
            LOG.d(
                "Forward phase %s(%s) -> %s",
                mail_from,
                copy_msg["From"],
                rcpt_to,
            )
            for is_delivered, smtp_status in handle_forward(
                envelope, copy_msg, rcpt_to
            ):
                res.append((is_delivered, smtp_status))

    for (is_success, smtp_status) in res:
        # Consider all deliveries successful if 1 delivery is successful
        if is_success:
            return smtp_status

    # Failed delivery for all, return the first failure
    return res[0][1]


class MailHandler:
    async def handle_DATA(self, server, session, envelope: Envelope):
        try:
            ret = self._handle(envelope)
            return ret
        except Exception:
            LOG.e(
                "email handling fail %s -> %s",
                envelope.mail_from,
                envelope.rcpt_tos,
            )
            return status.E404

    @newrelic.agent.background_task(application=newrelic_app)
    def _handle(self, envelope: Envelope):
        start = time.time()

        # generate a different message_id to keep track of an email lifecycle
        message_id = str(uuid.uuid4())
        set_message_id(message_id)

        LOG.i(
            "===>> New message, mail from %s, rctp tos %s ",
            envelope.mail_from,
            envelope.rcpt_tos,
        )

        app = new_app()
        with app.app_context():
            ret = handle(envelope)
            elapsed = time.time() - start
            LOG.i(
                "Finish mail from %s, rctp tos %s, takes %s seconds <<===",
                envelope.mail_from,
                envelope.rcpt_tos,
                elapsed,
            )
            newrelic.agent.record_custom_metric(
                "Custom/email_handler_time", elapsed, newrelic_app
            )
            newrelic.agent.record_custom_metric(
                "Custom/number_incoming_email", 1, newrelic_app
            )
            return ret


def main(port: int):
    """Use aiosmtpd Controller"""
    controller = Controller(MailHandler(), hostname="0.0.0.0", port=port)

    controller.start()
    LOG.d("Start mail controller %s %s", controller.hostname, controller.port)

    if LOAD_PGP_EMAIL_HANDLER:
        LOG.w("LOAD PGP keys")
        app = create_app()
        with app.app_context():
            load_pgp_public_keys()

    while True:
        time.sleep(2)


if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument(
        "-p", "--port", help="SMTP port to listen for", type=int, default=20381
    )
    args = parser.parse_args()

    LOG.i("Listen for port %s", args.port)
    main(port=args.port)