What does 504 mean?
SMTP 504 indicates an unimplemented parameter:
What it means:
The command is supported, but the specific parameter or option you used is not. The server cannot process this particular variation.
Common causes:
Unsupported authentication mechanism: AUTH method not available. Unsupported SMTP extension parameters: Options not implemented. Feature variations: Specific options disabled.
Typical message examples:
"504 Command parameter not implemented" "504 Authentication mechanism not supported" "504 Unrecognized authentication type"
Response:
Use an alternative parameter that the server supports. Check server capabilities via EHLO. Adjust configuration accordingly.
504 says "I support the command, but not that option." Find an alternative approach.
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