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504

Parameter Not Implemented

The command is supported but the specific parameter used is not implemented.

What does this error mean?

SMTP error 504 indicates a valid command with an unsupported parameter:

  • Authentication mechanism not supported
  • Encoding type not recognized
  • SMTP extension parameter unavailable
  • Feature parameter disabled by policy

Common Causes

  • lock
    Unsupported Auth Method

    The authentication mechanism (PLAIN, LOGIN, CRAM-MD5) isn't supported by the server.

  • code
    Invalid Encoding

    The specified encoding parameter isn't recognized or supported.

  • extension
    Extension Parameter

    An SMTP extension parameter that the server doesn't support.

    • How to Fix

    1. Try Different Authentication

    If related to AUTH, try a different authentication method (PLAIN, LOGIN, or CRAM-MD5).

    2. Check Server Capabilities

    Use EHLO to check what parameters the server supports before using them.

    3. Update Configuration

    Configure your mail server to use only standard, widely-supported parameters.

    Example response 
    504 5.5.4 Unrecognized authentication type
504 Command parameter not implemented
504 5.7.4 Unrecognized authentication mechanism

    Related SMTP Errors

    502 Command Not Implemented 500 Syntax Error 501 Syntax Error in Parameters 530 Authentication Required

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