Enhanced SMTP status code · RFC 3463 · IANA
5.1.2 Recipient domain cannot receive mail
The part right of the @ is not valid for mail: the destination system does not exist or cannot accept mail.
- Class: Permanent failure
Class 5: a permanent failure. Resending the same message will not help: something about the message, the sender or the destination must change (RFC 3463 §3.1). The registry says this code is only useful as a permanent failure.
- Subject: X.1 · Address
About the originator or destination address: syntax or validity. The sender can usually correct it and retry.
How 5.1.2 appears at providers
The exact text from the provider's documentation, as you see it in the bounce, and what it means.
Gmail
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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.
The recipient's domain was not found. Check its spelling. Check with Email DNS check.
What you can check here
Have the whole error message?
Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026