Enhanced status code

SMTP error X.7.8

Authentication credentials invalid

Updated Jul 1, 2026

The short answer

Authentication credentials invalid Common cause: Username, password, or token is incorrect or insufficient

Quick fix

Update SMTP credentials and authenticate again

This code is written X.7.8 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

Update SMTP credentials and authenticate again

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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