Fix "535 5.7.8": SMTP authentication failed (bad username or password)

Getting 535 5.7.8? It means SMTP authentication failed (bad username or password).

How to fix it

Check credentials; many providers require an app password, not your login password.

Prevent it

• Authenticate with SPF, DKIM and DMARC.
• Use a dedicated IP.
• Keep bounce and complaint rates low.

How Rainmail helps

Rainmail sends from your own domain on a dedicated, isolated IP with SPF, DKIM, DMARC, reverse-DNS and managed warm-up handled for you, a REST API, and an AI watching deliverability — and it welcomes senders SES, SendGrid and Mailchimp reject, from $8. Run the free checker or see plans.