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SMTP codes

SMTP 551 User not local

The recipient is not on this server, and it will not forward. Sometimes used for relay refusal.

551
Class
5xx · Permanent failure
Retried?
No, the message bounces
Defined in
RFC 5321

What to do

How it appears in a bounce

551 User not local

Paste the full bounce into the decoder — it finds every code and recipient and says what to check.

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