5.4.4: no 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.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.4.4
- 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
- Either side, depending on the cause. Start with the checks below that are yours.
- What the server says
5.4.4 Unable to route
What it means
X.4.4 means the routing information for the next hop was not available. RFC 3463's example is a DNS lookup that returns only an SOA record, which is what happens when a domain exists but publishes no MX or address records for mail. The RFC allows both classes. 5.4.4 means the sending server gave up because the domain cannot be routed to; 4.4.4 means it will keep trying in case the records appear. In bounces it usually points to a recipient domain with broken or missing DNS, a typo that happens to be a registered domain, or an internal routing rule with no destination.
Common causes
- The recipient domain has no MX record and no address record that mail could be sent to.
- A misspelled domain that exists but does not handle mail.
- DNS changes that are not yet visible to the sending server.
- An internal routing rule on a relay that has no destination.
How to fix it
- 01Run an MX lookup on the recipient domain.
- 02Check the address for a misspelled domain.
- 03If the domain is yours, publish MX records that point to your mail server.
- 04If you run the relay, check its routing or transport rules for that domain.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 5.1.2Recipient 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.
- 4.4.3DNS or directory lookup failed.The message could not be passed on because a directory server, most often DNS, did not answer; the lookup and the delivery are retried.
- 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.
Further reading
All 105 standard codesEvery code in the wikiPaste your own bounce