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SMTP codes

SMTP 504 Parameter not implemented

The command parameter, often the AUTH mechanism, is not supported.

504
Class
5xx · Permanent failure
Retried?
No, the message bounces
Defined in
RFC 5321

What to do

How it appears in a bounce

504 Parameter not implemented

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

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