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SMTP codes

SMTP 451 Local error in processing

The receiving server hit a temporary problem: a failed DNS lookup of your domain, an antispam check timeout, or greylisting. Temporary.

451
Class
4xx · Temporary failure
Retried?
Yes, the sending server retries
Defined in
RFC 5321

What to do

How it appears in a bounce

451 Local error in processing

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

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