Permanent failure — do not retry
SMTP 553 5.1.2
recipient domain not found
SMTP 553 5.1.2 means the domain in the recipient address does not exist or cannot accept mail. RFC 3463 defines X.1.2 as "bad destination system address". Gmail returns it as "We weren't able to find the recipient domain." Every address on that domain will fail, so remove it.
How it appears
553 5.1.2 We weren't able to find the recipient domain. Please check for any spelling errors, and make sure you didn't enter any spaces, periods, or other punctuation after the recipient's email address.
550 5.1.2 Host unknown (Name server: example.com: host not found)
What causes it
- A typo in the domain, such as gmial.com or a missing letter in a company domain.
- The domain has expired or was never registered.
- The domain exists but has no MX or A record, so mail has nowhere to go.
How to fix it
In order — try the first one first.
- Check the domain for an obvious typo and correct it if you can confirm the right address.
- Look up the domain's MX records. If there are none, no address there can receive mail.
- Remove the address. Retrying a domain that does not exist will not work.
Common questions
- What does SMTP 553 5.1.2 mean?
- SMTP 553 5.1.2 means the domain in the recipient address does not exist or cannot accept mail. RFC 3463 defines X.1.2 as "bad destination system address". Gmail returns it as "We weren't able to find the recipient domain." Every address on that domain will fail, so remove it.
- Should I retry a 553 5.1.2 error?
- No. 553 is a permanent failure, so the message will never be delivered no matter how many times you try. Remove the address — repeated sends to permanent failures are one of the main signals mailbox providers use to throttle a sender.
- How do I fix SMTP 553 5.1.2?
- Check the domain for an obvious typo and correct it if you can confirm the right address.
Other 553 replies
Last reviewed 2026-09-11