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Email stands as one of the most potent, dependable, and convenient modes of communication. Within any organization, the process of email communication relies on email clients such as Outlook Express, Microsoft Outlook, Lotus Notes, among others. However, there are instances when these email clients encounter issues, hindering their ability to send or receive messages.

This article delves into the SMTP error codes that can arise when you encounter difficulties sending or receiving email messages.

These error messages are often represented by numerical codes that can appear cryptic and challenging to decipher. When encountering SMTP, IMAP, POP, or any other errors, it becomes essential to understand the underlying causes and explore potential solutions to address these issues.

When encountering SMTP error messages, you’ll notice that they typically comprise three numerical components. Below, we’ve compiled a list of common SMTP error messages that may appear in cases of sending or receiving failures.

  • 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.

Resolving these SMTP error messages is crucial for ensuring the successful sending and receiving of emails.

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