In this article we'll learn why an email can bounce, how to interpret common email bounce-back error messages or codes, and steps to take to help solve your email issues.

We also have a new Bounceback Parser Tool that can help diagnose a bounced email.

Sometimes these email issues can be referred to in multiple ways, it's common to see them mentioned as a email bounceback or bounce-back message. You might also simply see them referred to as a email bounce, or a non delivery report.

If you've already read about what to do if an email is returned? You should already know some basic reasons for why an email bounceback error message or error code could prevent a successful delivery of your message.

Very briefly some of these common reasons would include a user's Inbox being full, an email account not existing, the IP address of the server or your ISP being blacklisted or blocked, the receiving server using Greylisting to defer the first few email attempts, or server sending limits being exceeded.

What is a Bounce Back?

A bounce back message occurs in the form of an email that is sent to your account after the failure to deliver a message that you have attempted to send. This message is generated either by your mail server or the mail server that was the destination of your email. Bounce back messages are a method to let you, the email sender, know that something has happened to disrupt the delivery of your email. This method of providing an error is standard on all email servers, but the actual text used in the messages can vary.

Importance of the Bounce Back Message

Providing the bounce back messages for helping to diagnose email issues is of the utmost importance. Bounce back messages can include vital information about the nature of the issue. Often, these messages will provide the information necessary for technical support to verify server issues as well the exact error type being reported by the server.

Why does e-mail bounceback?

If you were trying to send a letter to your friend via normal postal mail (snail mail), here are the steps that would need to be taken:

  • You fill out an envelope with your name and address up at the top-left, and your friend's name and address in the middle.
  • You place this envelope in a local postal drop-off box, or your own mailbox to be picked up.
  • Your envelope gets picked up by your local postal worker and taken to the local sorting facility.
  • Your envelope gets shipped to the remote sorting facility closest to your friend's address.
  • Your envelope gets picked up by the remote postal worker and taken to your friend's house.

An almost identical process is carried out when trying to deliver an email on the Internet:

  • Your email client fills out your name and email address into the From: header fields, and you enter in your friend's name and email address into the To: header fields.
  • You click send in your email client and wait for it to get picked up by the mail server.
  • Your email gets picked up by the email server set in your outgoing mail server settings.
  • Your email attempts to deliver from your email server, to your friends remote e-mail server.
  • Your email gets delivered by your friend's remote mail server into their email Inbox.

In the postal mail world, you'd typically get your envelope returned to you, stamped with return to sender on it. This could happen if either your local postal worker or the one on the remote end can't read your handwriting or the information is invalid.

A similar scenario also plays out in the email world. Mail servers use something called a MTA (Mail Transfer Agent) to handle email deliveries for the server. If you typed in something incorrectly in your friend's email address, or there is a temporary delivery problem with their mail server, that remote MTA will send a bounceback message to you with a specific email error message or error code explaining why the message couldn't be delivered at this time.

Soft bounce

If the friend you're trying to email has an email Inbox quota that has been exceeded, or their mail server is temporarily unavailable, your mail server will still try to deliver the email to their mail server. You would then receive a soft bounce from that remote server letting you know that the message was unable to be delivered, typically along with a specific reason.

A soft bounce is typically a temporary problem and you receive a bounceback message from the receipient's mail server alerting you of the issue so that you can try to send your message again at a later date.

Hard bounce

If you entered in your friend's e-mail address incorrectly and your mail server attempts to deliver the email to another remote server that doesn't handle e-mail for your friend. Then you will get back an almost immediate bounceback error.

A hard bounce can sometimes be a permanent problem, as it is essentially the remote mail server telling you that because the user you tried to e-mail doesn't exist on their server, it's not going to start working at a later time.

Blacklisted Bounce Back Messages

Blacklisting occurs when mail servers are flagged as being sources of spam. This may not necessarily be true, but if you see that your email is being blocked due to the server being blacklisted, then you will need to submit a request to have the server de-listed. To understand more about blacklisting and the action take if this happens, please see Why do Mail Servers get Blacklisted?

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