Email error codes

About those strange codes you get when a message is returned.

We’ve all received those email ‘bounce’ messages with curious codes to indicate the problem.

Sadly the text of these messages isn’t always very helpful. If you’re lucky there will be some explanatory text but otherwise you need to delve into the wonders of RFC2821 – the Extended SMTP specification.

The error codes comprise three digits separated by dots. Each number breaks down the type of error (or success).

1, 2 or 3 means the message was successfully sent or in the process of being sent. You won’t normally see these codes. Keep in mind that for the purposes of ESMTP codes ‘success’ means delivery to the receiving email servers, not the users mailbox or the recipient him/her self.

4 indicates a temporary problem – almost always you don’t have to do anything because the email system will automatically re-try.

5 is a permanent/fatal error – the message wasn’t delivered for various reasons.

The middle digit indicates the broad type of error.

The last digit is the specific error.

For our purposes we’re interested in the errors and here’s some of the more common ones. 

Replace the ‘X’ with either a 4 or 5 – most likely a 5 – a permanent error.



  • X.1.0 Other address status
  • X.1.1 Bad destination mailbox address
  • X.1.3 Bad destination mailbox address syntax
  • X.1.4 Destination mailbox address ambiguous
  • X.2.0 Other or undefined mailbox status
  • X.2.1 Mailbox disabled, not accepting messages
  • X.2.2 Mailbox full
  • X.2.3 Message length exceeds administrative limit.
  • X.3.1 Mail system full
  • X.3.4 Message too big for system