5.4.4 SMTP bounce: unable to route

What 5.4.4 means

The next hop for the message could not be determined from the routing information, so the message cannot be delivered.

Message text

Unable to route

Common causes of 5.4.4

• No MX or address record for the recipient domain
• Routing configuration error on the sending or receiving server

How to fix 5.4.4

1. Run MX lookup on the recipient domain.
2. Check the recipient domain's DNS for missing or misspelled records.

Check your domain

Check the MX records of the recipient domainRuns in your browser; nothing is uploaded.

Have the full bounce message? Paste it into the bounce code lookup and it will match the code and the provider for you. Open the bounce code lookup.

How to read 5.4.4

The second part, 5.4.4, is an enhanced status code (RFC 3463 §2) written class.subject.detail. Class 5 is a Permanent failure (5xx): the command was rejected and the sender should not repeat it unchanged (RFC 5321 §4.2.1; RFC 3463 §2).. Subject 4 is network and routing: a problem reaching or routing to the destination. The detail number refines the subject, and providers may define details of their own, which is why one code can read differently at Gmail, Microsoft and Yahoo.

Do not keep resending the same message: a permanent failure repeats until the cause is fixed. Correct the cause, then send a new message.

Official source: www.rfc-editor.org. Last verified 2026-10-20.

Related guides

• MX host does not resolve: causes and how to fix it
• How to set up MX records (priorities, null MX, migration)
• MX record points to a CNAME: why it breaks and the fix

Related codes

• 5.4.1 Microsoft: relay access denied
• 5.4.1 Microsoft: recipient rejected
• 5.4.14 Microsoft: routing loop
• 550 SMTP: mailbox unavailable
• 551 SMTP: user not local
• 552 SMTP: storage exceeded

FAQ

All bounce codes