Understanding SMTP Error Messages for Multiple Email Clients

Anju Chaudhary
Anju Chaudhary | Updated On - December 13, 2022 |

Read time 3 minutes

Email is the most powerful, reliable and convenient communication medium. In any organization, email communication is performed with the help of email clients like Outlook Express, Microsoft Outlook, Lotus Notes etc. But sometimes these email clients are unable to send or receive the email messages.

This article focuses on the SMTP error codes that flash whenever you are not able to send or receive the mail messages.

These error messages consist of mystic numbers that form some kind of incomprehensible code. Whenever any SMTP, IMAP, POP or any other error occur, it becomes necessary to know why the reason of error and what can be done to resolve the problem.

Whenever you receive SMTP error messages, you see that the SMTP error code consists of three numbers.  Below are some of the SMTP error messages that can pop up if sending/receiving fails.

  • 211 – A system status message.
  • 214 – A help message for a human reader follows
  • 220 – SMTP Service ready
  • 221 – Service closing.
  • 251 – The recipient is not local to the server, but the server will accept and forward the message.
  • 252 – The recipient cannot be verified but the server accepts the message and attempts delivery.
  • 354 – Start message input and end with <CRLF>.<CRLF>. This indicates that the server is ready to accept the message itself (after you have told it who it is from and where you want to go).
  • 421 – The service is not available and the connection will be closed.
  • 450 – The requested command failed because the user’s mailbox was unavailable (for example because it was locked). Try again later.
  • 451 – The command has been aborted due to a server error. Not your fault. Maybe let the admin know.
  • 452 – The command has been aborted because the server has insufficient system storage.
  • 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 system is configured to reject email from client system.
  • 550 – The requested command failed because the user’s mailbox was unavailable (for example because it was not found, or because the command was rejected for policy reasons).

  • 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.

These SMTP error messages need to be resolved for the successful sending /receiving of emails.

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