535 5.7.8 Authentication credentials invalid

Meaning

The authentication credentials provided were invalid.

Common causes

• Wrong username/password.
• Expired credentials.

How to fix

1. Update SMTP credentials.

Example bounce

535 5.7.8 Authentication credentials invalid

Related codes

• 451 4.7.24 Suspicious SPF record
• 550 5.7.26 Authentication failed (SPF/DKIM/DMARC)
• 534 5.7.9 Authentication mechanism is too weak