diff --git a/app/api/views/setting.py b/app/api/views/setting.py
index 1e7aad12..58e314d6 100644
--- a/app/api/views/setting.py
+++ b/app/api/views/setting.py
@@ -21,7 +21,9 @@ def setting_to_dict(user: User):
         if user.alias_generator == AliasGeneratorEnum.word.value
         else "uuid",
         "random_alias_default_domain": user.default_random_alias_domain(),
-        "sender_format": SenderFormatEnum.get_name(user.sender_format),
+        # return the default sender format (AT) in case user uses a non-supported sender format
+        "sender_format": SenderFormatEnum.get_name(user.sender_format)
+        or SenderFormatEnum.AT.name,
         "random_alias_suffix": AliasSuffixEnum.get_name(user.random_alias_suffix),
     }
 
diff --git a/app/models.py b/app/models.py
index a8aaf478..8b3ac509 100644
--- a/app/models.py
+++ b/app/models.py
@@ -329,10 +329,7 @@ class User(Base, ModelMixin, UserMixin, PasswordOracle):
     profile_picture = orm.relationship(File, foreign_keys=[profile_picture_id])
 
     # Specify the format for sender address
-    # John Wick - john at wick.com  -> 0
-    # john@wick.com via SimpleLogin -> 1
-    # John Wick - john(a)wick.com     -> 2
-    # John Wick - john@wick.com     -> 3
+    # for the full list, see SenderFormatEnum
     sender_format = sa.Column(
         sa.Integer, default="0", nullable=False, server_default="0"
     )