diff --git a/app/api/views/alias.py b/app/api/views/alias.py
index dd840750..27153f55 100644
--- a/app/api/views/alias.py
+++ b/app/api/views/alias.py
@@ -409,7 +409,7 @@ def create_contact_route(alias_id):
 
     contact_name, contact_email = full_address.display_name, full_address.address
 
-    contact_email = sanitize_email(contact_email)
+    contact_email = sanitize_email(contact_email, not_lower=True)
 
     # already been added
     contact = Contact.get_by(alias_id=alias.id, website_email=contact_email)
diff --git a/app/utils.py b/app/utils.py
index d90acfdf..6c884da0 100644
--- a/app/utils.py
+++ b/app/utils.py
@@ -66,9 +66,11 @@ def encode_url(url):
     return urllib.parse.quote(url, safe="")
 
 
-def sanitize_email(email_address: str) -> str:
+def sanitize_email(email_address: str, not_lower=False) -> str:
     if email_address:
-        return email_address.lower().strip().replace(" ", "").replace("\n", " ")
+        email_address = email_address.strip().replace(" ", "").replace("\n", " ")
+        if not not_lower:
+            email_address = email_address.lower()
     return email_address
 
 
diff --git a/cron.py b/cron.py
index ad91525a..2670bd99 100644
--- a/cron.py
+++ b/cron.py
@@ -656,7 +656,8 @@ def sanity_check():
             LOG.e("Contact %s reply-email not sanitized", contact)
 
         if (
-            sanitize_email(contact.website_email) != contact.website_email
+            sanitize_email(contact.website_email, not_lower=True)
+            != contact.website_email
             and contact.created_at > contact_email_sanity_date
         ):
             LOG.e("Contact %s website-email not sanitized", contact)
diff --git a/email_handler.py b/email_handler.py
index afedd912..4acd4b3f 100644
--- a/email_handler.py
+++ b/email_handler.py
@@ -180,7 +180,7 @@ def get_or_create_contact(from_header: str, mail_from: str, alias: Alias) -> Con
         # either reuse a contact with empty email or create a new contact with empty email
         contact_email = ""
 
-    contact_email = sanitize_email(contact_email)
+    contact_email = sanitize_email(contact_email, not_lower=True)
 
     if contact_name and "\x00" in contact_name:
         LOG.w("issue with contact name %s", contact_name)
@@ -300,10 +300,10 @@ def replace_header_when_forward(msg: Message, alias: Alias, header: str):
         full_addresses += address.parse_list(h)
 
     for full_address in full_addresses:
-        contact_email = sanitize_email(full_address.address)
+        contact_email = sanitize_email(full_address.address, not_lower=True)
 
         # no transformation when alias is already in the header
-        if contact_email == alias.email:
+        if contact_email.lower() == alias.email:
             new_addrs.append(full_address.full_spec())
             continue
 
@@ -1545,13 +1545,15 @@ def handle_bounce_reply_phase(envelope, msg: Message, email_log: EmailLog):
     bounce_info = get_mailbox_bounce_info(msg)
     if bounce_info:
         Bounce.create(
-            email=sanitize_email(contact.website_email),
+            email=sanitize_email(contact.website_email, not_lower=True),
             info=bounce_info.as_bytes().decode(),
             commit=True,
         )
     else:
         LOG.w("cannot get bounce info, debug at %s", save_email_for_debugging(msg))
-        Bounce.create(email=sanitize_email(contact.website_email), commit=True)
+        Bounce.create(
+            email=sanitize_email(contact.website_email, not_lower=True), commit=True
+        )
 
     # Store the bounced email
     # generate a name for the email