call strip() on rcpt_to just to be sure

email_handler.py

@@ -453,7 +453,7 @@ def handle_reply(envelope, smtp: SMTP, 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.lower()
+    reply_email = rcpt_to.lower().strip()
 
     # reply_email must end with EMAIL_DOMAIN
     if not reply_email.endswith(EMAIL_DOMAIN):