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.
• 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.