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500

Syntax Error

The server didn't understand the command. This indicates a protocol or software issue.

What does this error mean?

SMTP error 500 indicates a fundamental protocol problem:

  • The command sent was not recognized
  • Malformed SMTP communication
  • Software bug in the sending mail server
  • Protocol version mismatch

Common Causes

  • code
    Invalid Command

    The mail client sent a command the server doesn't understand.

  • bug_report
    Software Bug

    A bug in your email software is sending malformed commands.

  • sync_problem
    Protocol Mismatch

    Your mail server and the recipient's server have incompatible protocol versions.

    • How to Fix

    1. Update Mail Software

    Ensure your mail server software is up to date with the latest patches.

    2. Check Configuration

    Review your mail server configuration for any custom commands or extensions that might not be supported.

    3. Contact Administrator

    If the issue persists, contact your mail server administrator to investigate the SMTP logs.

    Example response 
    500 5.5.1 Command unrecognized
500 Syntax error, command unrecognized
500 Error: bad syntax

    Related SMTP Errors

    501 Syntax Error in Parameters 502 Command Not Implemented 503 Bad Sequence of Commands 504 Parameter Not Implemented

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