Generic SMTP destination-domain error
SMTP 5.1.2: bad destination system address
5.1.2 points to the destination system address—usually the recipient domain. Check the text after @ for a typo, then inspect that destination domain's DNS and mail routing.
A generic response can read:
550 5.1.2 Bad destination system address
Check the recipient destination domain
The 5.x.x result is permanent for this attempt. Correct a misspelling or wait for the recipient owner to repair routing, then send a new message.
Probable causes and owner
- Sender: the recipient domain was mistyped or has trailing punctuation.
- Recipient owner: the domain expired, lost delegation, or has invalid MX.
- Recipient provider: routing for the accepted domain is not provisioned.
- Receiver interpretation: the provider used this code for a more specific destination rule in the full response.
How to diagnose it
- Extract only the recipient domain and compare its spelling with a trusted source.
- Check registration/delegation and MX results.
- Confirm whether Null MX intentionally says the domain accepts no email.
- If you do not own the destination domain, send the evidence to the recipient through another channel.
- Retry only after the address or destination state changes.
Do not change the sender's SPF, DKIM, or DMARC solely for this generic destination-address result.
Frequently asked questions
What does SMTP 5.1.2 mean?
The destination system address is bad. This commonly points to the recipient domain rather than the sender's domain.
Which domain should I check?
Check the domain after the at-sign in the rejected recipient address. Do not enter the sender domain for this diagnostic.
Can the sender repair this error?
The sender can correct a typo. DNS or mail-routing changes require the recipient domain owner or its provider.
Related email diagnostics
Primary sources: IANA SMTP Enhanced Status Codes registry and RFC 3463 Enhanced Mail System Status Codes.