Received an Error Code after Sending a Mail? Understanding the SMTP Error Codes

Sometimes after sending an email, a system message will be displayed in your Mail List View with an SMTP error code. An SMTP error code is an error code sent from your provider (and displayed by BlueMail) that can give us some insight into why your provider denied your request to send an email.

Occasionally, your provider won’t be able to send an email because your email account needs to be re-authenticated (simply update your password) , sometimes it could because your providers server is temporarily unavailable, and there could be a few other reasons as well.

Below is a list of the Common Error Codes and reasons for why they happen.

Common Error Codes

  • 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 from your provider. Not your fault.
  • 452 – The command has been aborted because the providers server has insufficient system storage.
  • 454 – Authentication failed. Your email system must authenticate before sending mail (try to update your password within BlueMail)
  • 501 – A syntax error was encountered in command arguments.
  • 503 – The server has encountered a bad sequence of commands.
  • 504 – A command parameter is not implemented.
  • 521 – Connection to server rejected. This domain doesn’t accept mails. Could also be that the providers server is down.
  • 530 – Authentication is required. You must authenticate your email account before sending mail (try to update your password within BlueMail)
  • 535 – Authentication failed. You must authenticate your email account before sending mail (try to update your password within BlueMail)
  • 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.
  • 554 – Rejection from the Recipient Domain. Means ‘Not allowed’. The address in the “Sent From” or “Send To” headers appears to have insufficient submission rights, or is invalid, or is not authorized with the authentication used. Please check the recipient address.

    You can see a more extensive list here.

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