SMTP Error 535 - Authentication Failed

What does this error mean?

SMTP error 535 means your login credentials were rejected:

password

Wrong Password

The password you entered is incorrect or has been changed.

person

Wrong Username

The username format may be incorrect (try full email vs just username).

verified_user

2FA App Password

If 2FA is enabled, you need an app-specific password instead of your regular password.

lock

Account Locked

Too many failed attempts may have locked the account temporarily.

Double-check your username and password. Try logging into webmail to confirm they work.

If using Gmail, Outlook, or other providers with 2FA, generate an app-specific password.

Try using your full email address as username instead of just the username part.

If you've forgotten your password, use the provider's password reset feature.

Example response

535 5.7.8 Error: authentication failed
535 Incorrect authentication data
535 5.7.8 Username and Password not accepted