Fix "550 5.1.2": The recipient domain could not be found

Bouncing with 550 5.1.2? It means the recipient domain could not be found.

How to fix it

Verify the recipient domain has valid MX records and the address is correct.

Prevent it

• Authenticate with SPF, DKIM and DMARC.
• Send from 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, plus 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.