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SMTP Bounce Codes 

Have you ever heard the term ‘SMTP bounce codes’? Yes, in banks! In the banking sector, the term ‘bounced’ is used when the user information is incorrect, or there is some other issue with your account.

The word ‘Bounce’ is also used in the email platform in the SMTP server.

  • 2.XXX.YYY- this code means the sending was a success. The DNS server sends out a positive delivery action.
  • 4.XXX.YYY- Persistent Failure. The message sent is valid, but it causes a delay in sending the message. This code is termed as a soft bounce.
  • 5.XXX.YYY- Permanent Failure. Some changes to the messages should be made for the message delivery to be successful and check the SMTP bounce codes.
SMTP bounce codes

Some commonly occurring bounce codes on an email platform are:

  • 421- The transmission signal is closed, the service is not available. 
  • 450- The main action is not taken because of the unavailable mailbox.
  • 451- The requested action is aborted.
  • 452- Low on storage space, action not taken.
  • 500- The server could not recognize due to syntax error.
  • 501- A syntax error is formed in the command documents.
  • 502- The command is not implemented.
  • 503- The server found a bad sequence of commands.
  • 504- The parameter is not implemented.
  • 550- The user’s mailbox address is invalid.
  • 551- The recipient is not local to the server.
  • 552- The action was aborted due to exceeding storage space.
  • 553- The mailbox name is invalid.

To clear such errors, proceed with the steps given below:

  • Make sure the recipient has enough space left in the mailbox.
  • You can try and have an alternate mode of communication or try a different email address of the recipient.
  • Make sure you do not send an attachment that is more than 25 MB, exceeding the size limit may cause the message to slow down or not deliver at all. The message will be saved in your drafts if there is a bounce error.
  • Try and reduce the file size if the number of files is more in the attachment.
  • If you get the bounce message ’Permission denied’; it will show you the message: 554 service unavailable; Client host blocking using your name
  • If you come across such an error, it means that the recipient’s antivirus settings are blocking your emails from being sent to his/her computer.
  • The Antivirus thinks your messages have some corrupted files in it.
  • Make sure to scan your files before sending or ask the recipient to disable the antivirus application on his computer temporarily to fix the SMTP bounce codes.