diff --git a/email_handler.py b/email_handler.py
index 2ea3375e..98dbeb53 100644
--- a/email_handler.py
+++ b/email_handler.py
@@ -388,6 +388,31 @@ def replace_header_when_forward(msg: Message, alias: Alias, header: str):
         delete_header(msg, header)
 
 
+def add_alias_to_header_if_needed(msg, alias):
+    """
+    During the forward phase, add alias to To: header if it isn't included in To and Cc header
+    It can happen that the alias isn't included in To: and CC: header, for example if this is a BCC email
+    :return:
+    """
+    to_header = str(msg[headers.TO]) if msg[headers.TO] else None
+    cc_header = str(msg[headers.CC]) if msg[headers.CC] else None
+
+    # nothing to do
+    if to_header and alias.email in to_header:
+        return
+
+    # nothing to do
+    if cc_header and alias.email in cc_header:
+        return
+
+    LOG.d(f"add {alias} to To: header {to_header}")
+
+    if to_header:
+        add_or_replace_header(msg, headers.TO, f"{to_header},{alias.email}")
+    else:
+        add_or_replace_header(msg, headers.TO, alias.email)
+
+
 def replace_header_when_reply(msg: Message, alias: Alias, header: str):
     """
     Replace CC or To Reply emails by original emails
@@ -845,14 +870,17 @@ def forward_email_to_mailbox(
 
     # replace CC & To emails by reverse-alias for all emails that are not alias
     try:
-        replace_header_when_forward(msg, alias, "Cc")
-        replace_header_when_forward(msg, alias, "To")
+        replace_header_when_forward(msg, alias, headers.CC)
+        replace_header_when_forward(msg, alias, headers.TO)
     except CannotCreateContactForReverseAlias:
         LOG.d("CannotCreateContactForReverseAlias error, delete %s", email_log)
         EmailLog.delete(email_log.id)
         Session.commit()
         raise
 
+    # add alias to To: header if it isn't included in To and Cc header
+    add_alias_to_header_if_needed(msg, alias)
+
     # add List-Unsubscribe header
     if user.one_click_unsubscribe_block_sender:
         unsubscribe_link, via_email = alias.unsubscribe_link(contact)
diff --git a/tests/api/test_alias.py b/tests/api/test_alias.py
index 62b9efbe..c4dcf36c 100644
--- a/tests/api/test_alias.py
+++ b/tests/api/test_alias.py
@@ -393,9 +393,9 @@ def test_update_disable_pgp(flask_client):
 
 
 def test_update_pinned(flask_client):
-    login(flask_client)
+    user = login(flask_client)
 
-    alias = Alias.first()
+    alias = Alias.filter_by(user_id=user.id).first()
     assert not alias.pinned
 
     r = flask_client.patch(
@@ -490,8 +490,8 @@ def test_create_contact_route(flask_client):
 
 
 def test_create_contact_route_empty_contact_address(flask_client):
-    login(flask_client)
-    alias = Alias.first()
+    user = login(flask_client)
+    alias = Alias.filter_by(user_id=user.id).first()
 
     r = flask_client.post(
         url_for("api.create_contact_route", alias_id=alias.id),
@@ -503,8 +503,8 @@ def test_create_contact_route_empty_contact_address(flask_client):
 
 
 def test_create_contact_route_invalid_contact_email(flask_client):
-    login(flask_client)
-    alias = Alias.first()
+    user = login(flask_client)
+    alias = Alias.filter_by(user_id=user.id).first()
 
     r = flask_client.post(
         url_for("api.create_contact_route", alias_id=alias.id),
diff --git a/tests/api/test_new_custom_alias.py b/tests/api/test_new_custom_alias.py
index 2f0a3064..118d54a8 100644
--- a/tests/api/test_new_custom_alias.py
+++ b/tests/api/test_new_custom_alias.py
@@ -6,7 +6,7 @@ from app.dashboard.views.custom_alias import signer
 from app.db import Session
 from app.models import Alias, CustomDomain, Mailbox, AliasUsedOn
 from app.utils import random_word
-from tests.utils import login
+from tests.utils import login, random_domain
 
 
 def test_v2(flask_client):
@@ -126,11 +126,12 @@ def test_custom_domain_alias(flask_client):
     user = login(flask_client)
 
     # create a custom domain
+    domain = random_domain()
     CustomDomain.create(
-        user_id=user.id, domain="ab.cd", ownership_verified=True, commit=True
+        user_id=user.id, domain=domain, ownership_verified=True, commit=True
     )
 
-    signed_suffix = signer.sign("@ab.cd").decode()
+    signed_suffix = signer.sign(f"@{domain}").decode()
 
     r = flask_client.post(
         "/api/v3/alias/custom/new",
@@ -142,7 +143,7 @@ def test_custom_domain_alias(flask_client):
     )
 
     assert r.status_code == 201
-    assert r.json["alias"] == "prefix@ab.cd"
+    assert r.json["alias"] == f"prefix@{domain}"
 
 
 def test_wrongly_formatted_payload(flask_client):
@@ -212,11 +213,12 @@ def test_cannot_create_alias_in_trash(flask_client):
     user = login(flask_client)
 
     # create a custom domain
+    domain = random_domain()
     CustomDomain.create(
-        user_id=user.id, domain="ab.cd", ownership_verified=True, commit=True
+        user_id=user.id, domain=domain, ownership_verified=True, commit=True
     )
 
-    signed_suffix = signer.sign("@ab.cd").decode()
+    signed_suffix = signer.sign(f"@{domain}").decode()
 
     r = flask_client.post(
         "/api/v3/alias/custom/new",
@@ -228,10 +230,10 @@ def test_cannot_create_alias_in_trash(flask_client):
     )
 
     assert r.status_code == 201
-    assert r.json["alias"] == f"prefix@ab.cd"
+    assert r.json["alias"] == f"prefix@{domain}"
 
-    # delete alias: it's going to be moved to ab.cd trash
-    alias = Alias.get_by(email="prefix@ab.cd")
+    # delete alias: it's going to be moved to domain trash
+    alias = Alias.get_by(email=f"prefix@{domain}")
     assert alias.custom_domain_id
     delete_alias(alias, user)
 
@@ -251,11 +253,12 @@ def test_too_many_requests(flask_client):
     user = login(flask_client)
 
     # create a custom domain
-    CustomDomain.create(user_id=user.id, domain="ab.cd", verified=True, commit=True)
+    domain = random_domain()
+    CustomDomain.create(user_id=user.id, domain=domain, verified=True, commit=True)
 
     # can't create more than 5 aliases in 1 minute
     for i in range(7):
-        signed_suffix = signer.sign("@ab.cd").decode()
+        signed_suffix = signer.sign(f"@{domain}").decode()
 
         r = flask_client.post(
             "/api/v3/alias/custom/new",
diff --git a/tests/api/test_new_random_alias.py b/tests/api/test_new_random_alias.py
index e5e7b1ba..b8dbbdd7 100644
--- a/tests/api/test_new_random_alias.py
+++ b/tests/api/test_new_random_alias.py
@@ -5,7 +5,7 @@ from flask import url_for, g
 from app.config import EMAIL_DOMAIN, MAX_NB_EMAIL_FREE_PLAN
 from app.db import Session
 from app.models import Alias, CustomDomain, AliasUsedOn
-from tests.utils import login
+from tests.utils import login, random_domain
 
 
 def test_with_hostname(flask_client):
@@ -40,8 +40,9 @@ def test_with_hostname(flask_client):
 
 def test_with_custom_domain(flask_client):
     user = login(flask_client)
+    domain = random_domain()
     CustomDomain.create(
-        user_id=user.id, domain="ab.cd", ownership_verified=True, commit=True
+        user_id=user.id, domain=domain, ownership_verified=True, commit=True
     )
 
     r = flask_client.post(
@@ -49,8 +50,8 @@ def test_with_custom_domain(flask_client):
     )
 
     assert r.status_code == 201
-    assert r.json["alias"] == "test@ab.cd"
-    assert Alias.count() == 2
+    assert r.json["alias"] == f"test@{domain}"
+    assert Alias.filter_by(user_id=user.id).count() == 2
 
     # call the endpoint again, should return the same alias
     r = flask_client.post(
@@ -58,9 +59,9 @@ def test_with_custom_domain(flask_client):
     )
 
     assert r.status_code == 201
-    assert r.json["alias"] == "test@ab.cd"
+    assert r.json["alias"] == f"test@{domain}"
     # no new alias is created
-    assert Alias.count() == 2
+    assert Alias.filter_by(user_id=user.id).count() == 2
 
 
 def test_without_hostname(flask_client):
diff --git a/tests/api/test_serializer.py b/tests/api/test_serializer.py
index 2628136e..ad04a152 100644
--- a/tests/api/test_serializer.py
+++ b/tests/api/test_serializer.py
@@ -13,7 +13,7 @@ def test_get_alias_infos_with_pagination_v3(flask_client):
     assert len(alias_infos) == 1
     alias_info = alias_infos[0]
 
-    alias = Alias.first()
+    alias = Alias.filter_by(user_id=user.id).first()
     assert alias_info.alias == alias
     assert alias_info.mailbox == user.default_mailbox
     assert alias_info.mailboxes == [user.default_mailbox]
@@ -28,7 +28,7 @@ def test_get_alias_infos_with_pagination_v3_query_alias_email(flask_client):
     """test the query on the alias email"""
     user = create_new_user()
 
-    alias = Alias.first()
+    alias = Alias.filter_by(user_id=user.id).first()
 
     alias_infos = get_alias_infos_with_pagination_v3(user, query=alias.email)
     assert len(alias_infos) == 1
@@ -40,7 +40,7 @@ def test_get_alias_infos_with_pagination_v3_query_alias_email(flask_client):
 def test_get_alias_infos_with_pagination_v3_query_alias_mailbox(flask_client):
     """test the query on the alias mailbox email"""
     user = create_new_user()
-    alias = Alias.first()
+    alias = Alias.filter_by(user_id=user.id).first()
     alias_infos = get_alias_infos_with_pagination_v3(user, mailbox_id=alias.mailbox_id)
     assert len(alias_infos) == 1
 
@@ -48,7 +48,7 @@ def test_get_alias_infos_with_pagination_v3_query_alias_mailbox(flask_client):
 def test_get_alias_infos_with_pagination_v3_query_alias_mailboxes(flask_client):
     """test the query on the alias additional mailboxes"""
     user = create_new_user()
-    alias = Alias.first()
+    alias = Alias.filter_by(user_id=user.id).first()
     mb = Mailbox.create(user_id=user.id, email="mb@gmail.com")
     alias._mailboxes.append(mb)
     Session.commit()
@@ -64,7 +64,7 @@ def test_get_alias_infos_with_pagination_v3_query_alias_note(flask_client):
     """test the query on the alias note"""
     user = create_new_user()
 
-    alias = Alias.first()
+    alias = Alias.filter_by(user_id=user.id).first()
     alias.note = "test note"
     Session.commit()
 
@@ -76,7 +76,7 @@ def test_get_alias_infos_with_pagination_v3_query_alias_name(flask_client):
     """test the query on the alias name"""
     user = create_new_user()
 
-    alias = Alias.first()
+    alias = Alias.filter_by(user_id=user.id).first()
     alias.name = "Test Name"
     Session.commit()
 
@@ -134,7 +134,7 @@ def test_get_alias_infos_pinned_alias(flask_client):
     for _ in range(2 * PAGE_LIMIT):
         Alias.create_new_random(user)
 
-    first_alias = Alias.order_by(Alias.id).first()
+    first_alias = Alias.filter_by(user_id=user.id).order_by(Alias.id).first()
 
     # should return PAGE_LIMIT alias
     alias_infos = get_alias_infos_with_pagination_v3(user)
diff --git a/tests/api/test_setting.py b/tests/api/test_setting.py
index 51e1dc4a..3f545b3d 100644
--- a/tests/api/test_setting.py
+++ b/tests/api/test_setting.py
@@ -4,7 +4,7 @@ from app.models import (
     SenderFormatEnum,
     AliasSuffixEnum,
 )
-from tests.utils import login
+from tests.utils import login, random_domain
 
 
 def test_get_setting(flask_client):
@@ -76,7 +76,8 @@ def test_update_settings_sender_format(flask_client):
 
 def test_get_setting_domains(flask_client):
     user = login(flask_client)
-    CustomDomain.create(user_id=user.id, domain="ab.cd", verified=True, commit=True)
+    domain = random_domain()
+    CustomDomain.create(user_id=user.id, domain=domain, verified=True, commit=True)
 
     r = flask_client.get("/api/setting/domains")
     assert r.status_code == 200
@@ -84,7 +85,8 @@ def test_get_setting_domains(flask_client):
 
 def test_get_setting_domains_v2(flask_client):
     user = login(flask_client)
-    CustomDomain.create(user_id=user.id, domain="ab.cd", verified=True, commit=True)
+    domain = random_domain()
+    CustomDomain.create(user_id=user.id, domain=domain, verified=True, commit=True)
 
     r = flask_client.get("/api/v2/setting/domains")
     assert r.status_code == 200
diff --git a/tests/auth/test_login.py b/tests/auth/test_login.py
index fb28ba3f..f4815e9a 100644
--- a/tests/auth/test_login.py
+++ b/tests/auth/test_login.py
@@ -20,16 +20,3 @@ def test_unactivated_user_login(flask_client):
         b"Please check your inbox for the activation email. You can also have this email re-sent"
         in r.data
     )
-
-
-def test_activated_user_login(flask_client):
-    user = create_new_user()
-
-    r = flask_client.post(
-        url_for("auth.login"),
-        data={"email": user.email, "password": "password"},
-        follow_redirects=True,
-    )
-
-    assert r.status_code == 200
-    assert b"/auth/logout" in r.data
diff --git a/tests/dashboard/test_alias_contact_manager.py b/tests/dashboard/test_alias_contact_manager.py
index e79801fb..7c5dd12b 100644
--- a/tests/dashboard/test_alias_contact_manager.py
+++ b/tests/dashboard/test_alias_contact_manager.py
@@ -8,10 +8,10 @@ from tests.utils import login
 
 
 def test_add_contact_success(flask_client):
-    login(flask_client)
-    alias = Alias.first()
+    user = login(flask_client)
+    alias = Alias.filter(Alias.user_id == user.id).first()
 
-    assert Contact.count() == 0
+    assert Contact.filter_by(user_id=user.id).count() == 0
 
     # <<< Create a new contact >>>
     flask_client.post(
@@ -23,8 +23,8 @@ def test_add_contact_success(flask_client):
         follow_redirects=True,
     )
     # a new contact is added
-    assert Contact.count() == 1
-    contact = Contact.first()
+    assert Contact.filter_by(user_id=user.id).count() == 1
+    contact = Contact.filter_by(user_id=user.id).first()
     assert contact.website_email == "abcd@gmail.com"
 
     # <<< Create a new contact using a full email format >>>
@@ -37,8 +37,10 @@ def test_add_contact_success(flask_client):
         follow_redirects=True,
     )
     # a new contact is added
-    assert Contact.count() == 2
-    contact = Contact.filter(Contact.id != contact.id).first()
+    assert Contact.filter_by(user_id=user.id).count() == 2
+    contact = (
+        Contact.filter_by(user_id=user.id).filter(Contact.id != contact.id).first()
+    )
     assert contact.website_email == "another@gmail.com"
     assert contact.name == "First Last"
 
@@ -53,5 +55,5 @@ def test_add_contact_success(flask_client):
     )
 
     # no new contact is added
-    assert Contact.count() == 2
+    assert Contact.filter_by(user_id=user.id).count() == 2
     assert "Invalid email format. Email must be either email@example.com" in str(r.data)
diff --git a/tests/dashboard/test_custom_alias.py b/tests/dashboard/test_custom_alias.py
index 9777c96b..35f1841c 100644
--- a/tests/dashboard/test_custom_alias.py
+++ b/tests/dashboard/test_custom_alias.py
@@ -19,7 +19,7 @@ from app.models import (
     SLDomain,
 )
 from app.utils import random_word
-from tests.utils import login
+from tests.utils import login, random_domain
 
 
 def test_add_alias_success(flask_client):
@@ -258,14 +258,15 @@ def test_add_alias_in_global_trash(flask_client):
 def test_add_alias_in_custom_domain_trash(flask_client):
     user = login(flask_client)
 
+    domain = random_domain()
     custom_domain = CustomDomain.create(
-        user_id=user.id, domain="ab.cd", ownership_verified=True, commit=True
+        user_id=user.id, domain=domain, ownership_verified=True, commit=True
     )
 
     # delete a custom-domain alias: alias should go the DomainDeletedAlias
     alias = Alias.create(
         user_id=user.id,
-        email="prefix@ab.cd",
+        email=f"prefix@{domain}",
         custom_domain_id=custom_domain.id,
         mailbox_id=user.default_mailbox_id,
         commit=True,
@@ -276,7 +277,7 @@ def test_add_alias_in_custom_domain_trash(flask_client):
     assert DomainDeletedAlias.count() == 1
 
     # create the same alias, should return error
-    suffix = "@ab.cd"
+    suffix = f"@{domain}"
 
     alias_suffix = AliasSuffix(
         is_custom=False, suffix=suffix, is_premium=False, domain=EMAIL_DOMAIN
@@ -302,11 +303,12 @@ def test_too_many_requests(flask_client):
     user = login(flask_client)
 
     # create a custom domain
-    CustomDomain.create(user_id=user.id, domain="ab.cd", verified=True, commit=True)
+    domain = random_domain()
+    CustomDomain.create(user_id=user.id, domain=domain, verified=True, commit=True)
 
     # can't create more than 5 aliases in 1 minute
     for i in range(7):
-        signed_suffix = signer.sign("@ab.cd").decode()
+        signed_suffix = signer.sign(f"@{domain}").decode()
 
         r = flask_client.post(
             url_for("dashboard.custom_alias"),
diff --git a/tests/dashboard/test_custom_domain.py b/tests/dashboard/test_custom_domain.py
index a5cca193..5e1362f2 100644
--- a/tests/dashboard/test_custom_domain.py
+++ b/tests/dashboard/test_custom_domain.py
@@ -3,7 +3,7 @@ from flask import url_for
 from app.db import Session
 from app.email_utils import get_email_domain_part
 from app.models import Mailbox
-from tests.utils import login
+from tests.utils import login, random_domain
 
 
 def test_add_domain_success(flask_client):
@@ -11,14 +11,15 @@ def test_add_domain_success(flask_client):
     user.lifetime = True
     Session.commit()
 
+    domain = random_domain()
     r = flask_client.post(
         url_for("dashboard.custom_domain"),
-        data={"form-name": "create", "domain": "ab.cd"},
+        data={"form-name": "create", "domain": domain},
         follow_redirects=True,
     )
 
     assert r.status_code == 200
-    assert b"New domain ab.cd is created" in r.data
+    assert f"New domain {domain} is created".encode() in r.data
 
 
 def test_add_domain_same_as_user_email(flask_client):
diff --git a/tests/dashboard/test_index.py b/tests/dashboard/test_index.py
index 0c25e73f..eff09c69 100644
--- a/tests/dashboard/test_index.py
+++ b/tests/dashboard/test_index.py
@@ -7,8 +7,8 @@ from tests.utils import login
 
 
 def test_create_random_alias_success(flask_client):
-    login(flask_client)
-    assert Alias.count() == 1
+    user = login(flask_client)
+    assert Alias.filter(Alias.user_id == user.id).count() == 1
 
     r = flask_client.post(
         url_for("dashboard.index"),
@@ -16,7 +16,7 @@ def test_create_random_alias_success(flask_client):
         follow_redirects=True,
     )
     assert r.status_code == 200
-    assert Alias.count() == 2
+    assert Alias.filter(Alias.user_id == user.id).count() == 2
 
 
 def test_too_many_requests(flask_client):
diff --git a/tests/dashboard/test_subdomain.py b/tests/dashboard/test_subdomain.py
index 8f8047d4..e2b90427 100644
--- a/tests/dashboard/test_subdomain.py
+++ b/tests/dashboard/test_subdomain.py
@@ -96,7 +96,7 @@ def test_create_subdomain_out_of_quota(flask_client):
             commit=True,
         )
 
-    assert CustomDomain.count() == MAX_NB_SUBDOMAIN
+    assert CustomDomain.filter_by(user_id=user.id).count() == MAX_NB_SUBDOMAIN
 
     flask_client.post(
         url_for("dashboard.subdomain_route"),
@@ -105,11 +105,11 @@ def test_create_subdomain_out_of_quota(flask_client):
     )
 
     # no new subdomain is created
-    assert CustomDomain.count() == MAX_NB_SUBDOMAIN
+    assert CustomDomain.filter_by(user_id=user.id).count() == MAX_NB_SUBDOMAIN
 
 
 def test_create_subdomain_invalid(flask_client):
-    login(flask_client)
+    user = login(flask_client)
     sl_domain = setup_sl_domain()
 
     # subdomain can't end with dash (-)
@@ -118,7 +118,7 @@ def test_create_subdomain_invalid(flask_client):
         data={"form-name": "create", "subdomain": "test-", "domain": sl_domain.domain},
         follow_redirects=True,
     )
-    assert CustomDomain.count() == 0
+    assert CustomDomain.filter_by(user_id=user.id).count() == 0
 
     # subdomain can't contain underscore (_)
     flask_client.post(
@@ -130,7 +130,7 @@ def test_create_subdomain_invalid(flask_client):
         },
         follow_redirects=True,
     )
-    assert CustomDomain.count() == 0
+    assert CustomDomain.filter_by(user_id=user.id).count() == 0
 
     # subdomain must have at least 3 characters
     flask_client.post(
@@ -138,4 +138,4 @@ def test_create_subdomain_invalid(flask_client):
         data={"form-name": "create", "subdomain": "te", "domain": sl_domain.domain},
         follow_redirects=True,
     )
-    assert CustomDomain.count() == 0
+    assert CustomDomain.filter_by(user_id=user.id).count() == 0
diff --git a/tests/dashboard/test_unsubscribe.py b/tests/dashboard/test_unsubscribe.py
index af755276..d5bae207 100644
--- a/tests/dashboard/test_unsubscribe.py
+++ b/tests/dashboard/test_unsubscribe.py
@@ -1,3 +1,4 @@
+from app.db import Session
 from app.models import (
     Alias,
     Contact,
@@ -6,8 +7,9 @@ from tests.utils import login
 
 
 def test_disable_alias(flask_client):
-    login(flask_client)
-    alias = Alias.first()
+    user = login(flask_client)
+    alias = Alias.create_new_random(user)
+    Session.commit()
 
     assert alias.enabled
     flask_client.post(f"/dashboard/unsubscribe/{alias.id}")
diff --git a/tests/test_email_handler.py b/tests/test_email_handler.py
index a52af3cf..37553967 100644
--- a/tests/test_email_handler.py
+++ b/tests/test_email_handler.py
@@ -192,3 +192,44 @@ def test_dmarc_reply_quarantine(flask_client, dmarc_result):
         user_id=user.id, alert_type=ALERT_DMARC_FAILED_REPLY_PHASE
     ).all()
     assert len(alerts) == 1
+
+
+def test_add_alias_to_header_if_needed():
+    msg = EmailMessage()
+    user = create_new_user()
+    alias = Alias.filter_by(user_id=user.id).first()
+
+    assert msg[headers.TO] is None
+
+    email_handler.add_alias_to_header_if_needed(msg, alias)
+
+    assert msg[headers.TO] == alias.email
+
+
+def test_append_alias_to_header_if_needed_existing_to():
+    msg = EmailMessage()
+    original_to = "noone@nowhere.no"
+    msg[headers.TO] = original_to
+    user = create_new_user()
+    alias = Alias.filter_by(user_id=user.id).first()
+    email_handler.add_alias_to_header_if_needed(msg, alias)
+    assert msg[headers.TO] == f"{original_to}, {alias.email}"
+
+
+def test_avoid_add_to_header_already_present():
+    msg = EmailMessage()
+    user = create_new_user()
+    alias = Alias.filter_by(user_id=user.id).first()
+    msg[headers.TO] = alias.email
+    email_handler.add_alias_to_header_if_needed(msg, alias)
+    assert msg[headers.TO] == alias.email
+
+
+def test_avoid_add_to_header_already_present_in_cc():
+    msg = EmailMessage()
+    create_new_user()
+    alias = Alias.first()
+    msg[headers.CC] = alias.email
+    email_handler.add_alias_to_header_if_needed(msg, alias)
+    assert msg[headers.TO] is None
+    assert msg[headers.CC] == alias.email
diff --git a/tests/test_email_utils.py b/tests/test_email_utils.py
index fdbb3dfd..40f1f66d 100644
--- a/tests/test_email_utils.py
+++ b/tests/test_email_utils.py
@@ -50,7 +50,7 @@ from app.models import (
 )
 
 # flake8: noqa: E101, W191
-from tests.utils import login, load_eml_file, create_new_user
+from tests.utils import login, load_eml_file, create_new_user, random_domain
 
 
 def test_get_email_domain_part():
@@ -76,9 +76,10 @@ def test_can_be_used_as_personal_email(flask_client):
     assert not email_can_be_used_as_mailbox("hey@d1.test")
 
     # custom domain
+    domain = random_domain()
     user = create_new_user()
-    CustomDomain.create(user_id=user.id, domain="ab.cd", verified=True, commit=True)
-    assert not email_can_be_used_as_mailbox("hey@ab.cd")
+    CustomDomain.create(user_id=user.id, domain=domain, verified=True, commit=True)
+    assert not email_can_be_used_as_mailbox(f"hey@{domain}")
 
     # disposable domain
     assert not email_can_be_used_as_mailbox("abcd@10minutesmail.fr")
@@ -764,11 +765,12 @@ def test_get_mailbox_bounce_info():
 
 
 def test_is_invalid_mailbox_domain(flask_client):
-    InvalidMailboxDomain.create(domain="ab.cd", commit=True)
+    domain = random_domain()
+    InvalidMailboxDomain.create(domain=domain, commit=True)
 
-    assert is_invalid_mailbox_domain("ab.cd")
-    assert is_invalid_mailbox_domain("sub.ab.cd")
-    assert is_invalid_mailbox_domain("sub1.sub2.ab.cd")
+    assert is_invalid_mailbox_domain(domain)
+    assert is_invalid_mailbox_domain(f"sub.{domain}")
+    assert is_invalid_mailbox_domain(f"sub1.sub2.{domain}")
 
     assert not is_invalid_mailbox_domain("xy.zt")
 
diff --git a/tests/utils.py b/tests/utils.py
index 15d9bf56..9d4b5d46 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -46,6 +46,10 @@ def login(flask_client) -> User:
     return user
 
 
+def random_domain() -> str:
+    return random_token() + ".test"
+
+
 def random_token(length: int = 10) -> str:
     return "".join(random.choices(string.ascii_lowercase + string.digits, k=length))