5.1.2: recipient domain cannot receive mail
The part of the address after the @ names a domain that does not exist or cannot accept mail, so the message cannot be delivered there.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.1.2
- Provider
- Standard SMTP codes
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
5.1.2 Bad destination system address
What it means
Where 5.1.1 says the mailbox is unknown, 5.1.2 says the whole destination is wrong: the domain to the right of the @ does not exist, or it has no mail server able to take the message. RFC 3463 reserves it for permanent failures, so the message is returned. It can come from the sender's own outgoing server, which looked the domain up in DNS and found nothing usable, or from a relay that refuses a domain it does not serve. A misspelled domain is the most frequent reason. A 4.1.2 form is rare; when it appears, the sending server retries.
Common causes
- A misspelled domain, such as gmial.com, or a missing country ending.
- A domain that has expired or was never registered.
- A domain whose DNS has no MX record and no address record a server could deliver to.
- A relay that does not accept mail for that domain.
How to fix it
- 01Check the spelling of the domain in the bounce.
- 02Run an MX lookup on the domain to see whether it publishes a mail server.
- 03If the domain is yours or a customer's, fix its MX records at the DNS host.
- 04Remove addresses at domains that no longer exist from your list.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 5.1.1Mailbox does not exist.The recipient's domain accepts mail, but the mailbox named before the @ does not exist there, so the message was refused and will not be delivered.
- 556 5.1.10Recipient domain has a null MX.The recipient's domain publishes a null MX record, its formal statement that it never receives email, so the message was refused at once without any delivery attempt.
- 5.4.4No route to the recipient domain.The mail system could not work out where to send the message next, because DNS gave no usable mail server for the recipient domain.
- 550Mailbox unavailable.The receiving server permanently refused the message for this recipient: the mailbox does not exist, cannot be reached, or the server rejected the message by policy.
5.1.2 at other providers
Further reading
All 105 standard codesEvery code in the wikiPaste your own bounce