List of SMTP Error Codes

• 211 – System Status Message
• 214 – Help message for human reader
• 220 – SMTP read only
• 221- Service closing
• 250 – Requested action taken and completed.
• 251 – The recipient is not local to the server, but the server accepts the message and attempts delivery.
• 252 – The recipient cannot be verified, the server accepts the message and attempts delivery.
• 354 – Start message input and end with.. The server is ready to accept the message once it has been told who it is from and where it goes.
• 421 – The service is not available and the connection will be closed.
• 450 – The requested command failed because the user’s mailbox was unavailable.
• 451 – The command has been aborted due to a server error.
• 452 – The command has been aborted because the server has insufficient system storage.
• 455 – The server cannot deal with the command at this time.
• 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.
• 521 – This host never accepts mail
• 541 – The message could not be delivered for policy reasons. This message is generally caused by a spam filter)
•  550 – The requested command failed because the user’s mailbox was unavailable. This message is generally cased by the mailbox not existing or a policy is preventing delivery.
• 551 – The recipient is not local to the server. The server will provide a forward address to try.
• 552 – The action was aborted due to the exceeded storage allocation.
• 553 – The command was aborted because the mailbox name is invalid.
• 554 – The transaction failed. Generic error.
• 555 – The server does not recognize the email address format and deliver is not possible.
• 556 – The message would have to be forwarded, but the receiving server will reject it.