Enhanced status code Permanent

SMTP error X.5.4

Invalid command arguments

Updated Jul 1, 2026

The short answer

Invalid command arguments Common cause: Valid SMTP command contained unsupported / invalid values

Quick fix

Correct the command parameters

5 - Permanent. The server will not try again. Fix the cause before you resend.
This code is written X.5.4 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

Correct the command parameters

Related codes

X.5.0 Other or undefined protocol status X.5.1 Invalid command X.5.2 Syntax error X.5.3 Too many recipients X.5.5 Wrong protocol version X.5.6 Authentication exchange line too long
All SMTP error codes
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