SMTP error X.2.4
Mailing list expansion problem
Updated Jul 1, 2026
The short answer
Mailing list expansion problem Common cause: Distribution list could not expand its members
Quick fix
Retry later or contact the list administrator
2 - Success. Not an error - the server accepted or completed the action.
This code is written X.2.4 because the reason is the same whether the failure
is temporary (a 4 first digit) or permanent (a 5). Read the first digit of your
own bounce to know which applies.
How to fix it
Retry later or contact the list administrator