SMTP 551: user not local, please try another address
The receiving server doesn't host this recipient anymore and refuses to forward the message. The reply may include a new address to try.
What 551 means
RFC 5321 defines 551 as "User not local; please try <forward-path>". Section 3.4 explains when servers use it: a server that knows a recipient's address has changed may reject the message and give address-updating information with a 551, or simply reject it with a 550 and no details. A server can also forward silently and accept the message instead.
Many servers never send 551, because it reveals where a person's mail now goes. RFC 5321 asks implementations to let administrators disable or restrict it for that reason. When you do see one, it usually follows a move: someone changed jobs, a company changed domains, or an old mail server was retired.
The message was not delivered. If the reply names a new address, confirm it with the recipient before you resend, because the reply alone doesn't prove the new address is right. If no address is given, contact the person another way.
Likely causes
- The recipient moved to a new address or provider.
- The domain moved its mail to a different server and the old one rejects mail it no longer hosts.
How to fix it
If you sent the message
- If the bounce names a new address, confirm it with the recipient, then resend.
- Update the address in your contacts and mailing lists.
If you're the recipient or their admin
- Set up forwarding or an auto-reply on the old address while people update their records.
- If you moved providers, check your MX records point only to the new service.
Frequently asked questions
Was my message forwarded after a 551?
No. A 551 is a permanent rejection. The server is telling you where the recipient might be now, but it did not pass your message on.
Why don't more servers use 551?
Because it discloses a person's new address. RFC 5321 asks servers that support 551 to let administrators disable or restrict it, and many reject with a plain 550 instead.
Sources
- RFC 5321: Simple Mail Transfer Protocol (reply codes, section 4.2)
- RFC 5321, section 3.4: Forwarding for address correction or updating
Provider messages are quoted as the provider publishes them. Servers can change their wording, so the bounce you received may differ slightly.
Related codes
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