Enhanced status code

SMTP error X.1.7

Bad sender mailbox address syntax

Updated Jul 1, 2026

The short answer

Bad sender mailbox address syntax Common cause: Sender address is malformed

Quick fix

Correct the From / envelope sender address

This code is written X.1.7 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 From / envelope sender address

Related codes

X.1.0 Other address status X.1.1 Bad destination mailbox address X.1.2 Bad destination system address X.1.3 Bad destination mailbox address syntax X.1.4 Destination mailbox address ambiguous X.1.5 Destination address valid
All SMTP error codes
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