Enhanced status code

SMTP error X.7.9

Authentication mechanism too weak

Updated Jul 1, 2026

The short answer

Authentication mechanism too weak Common cause: Server requires a stronger AUTH method

Quick fix

Switch to a stronger supported authentication mechanism

This code is written X.7.9 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

Switch to a stronger supported authentication mechanism

Related codes

X.7.0 Other or undefined security status X.7.1 Delivery not authorized X.7.2 Mailing list expansion prohibited X.7.3 Security conversion required but impossible X.7.4 Security features not supported X.7.5 Cryptographic failure
All SMTP error codes
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