What are the SMTP Error Codes and what do they mean?

Possible 5xx codes

  • 500 - The server could not recognize the command due to a syntax error.
  • 501 - A syntax error was encountered in command arguments.
  • 502 - This command is not implemented.
  • 503 - The server has encountered a bad sequence of commands.
  • 504 - A command parameter is not implemented.
  • 550 - No mailbox by that name is currently available (for example because it was not found, or because the command was rejected for policy reasons including a full mailbox. Please Clear the callout cache after the mailbox has been emptied).
  • 551 - The recipient is not local to the server. The server then gives a forward address to try.
  • 552 - The action was aborted due to exceeded storage allocation.
  • 553 - The command was aborted because the mailbox name is invalid.
  • 554 - The transaction failed. Blame it on the weather.

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