diff --git a/core/mail/protocol.py b/core/mail/protocol.py
index 3639989..8fa2c3b 100644
--- a/core/mail/protocol.py
+++ b/core/mail/protocol.py
@@ -220,7 +220,7 @@ def receive_email(envelope, log=None):
 
     if Email.objects.filter(reference=header_message_id).exists():  # break before issue thread is created
         log.warning("Email already exists")
-        raise Exception("Email already exists")
+        raise SpecialMailException("Email already exists")
 
     recipient = envelope.rcpt_tos[0].lower() if envelope.rcpt_tos else header_to.lower()
     sender = envelope.mail_from if envelope.mail_from else header_from