Enhanced status code

SMTP error X.3.3

System not capable of selected features

Updated Jul 1, 2026

The short answer

System not capable of selected features Common cause: Destination cannot support a requested mail feature

Quick fix

Remove or change the unsupported feature

This code is written X.3.3 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

Remove or change the unsupported feature

Related codes

X.3.0 Other or undefined mail system status X.3.1 Mail system full X.3.2 System not accepting network messages X.3.4 Message too big for system X.3.5 System incorrectly configured X.3.6 Requested priority changed
All SMTP error codes
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