diff --git a/hosts/bicep/services/matrix/smtp-authenticator/smtp_auth_provider.py b/hosts/bicep/services/matrix/smtp-authenticator/smtp_auth_provider.py
index ac6694f..ae4e04d 100644
--- a/hosts/bicep/services/matrix/smtp-authenticator/smtp_auth_provider.py
+++ b/hosts/bicep/services/matrix/smtp-authenticator/smtp_auth_provider.py
@@ -5,6 +5,7 @@ from smtplib import SMTP_SSL as SMTP
 import synapse
 from synapse import module_api
 
+import re
 
 class SMTPAuthProvider:
     def __init__(self, config: dict, api: module_api):
@@ -27,6 +28,10 @@ class SMTPAuthProvider:
         if login_type != "m.login.password":
             return None
 
+        # Convert `@username:server` to `username`
+        match = re.match(r'^@([\da-z\-\.=_\/\+]+):[\w\d\.:\[\]]+$', username)
+        username = match.group(1) if match else username
+
         result = False
         with SMTP(self.config["smtp_host"]) as smtp:
             password = login_dict.get("password")