How to Read Email Bounce Backs and Errors

Bounce backs and error codes for email can be very mysterious and misleading. To help with that we have started a new series on the blog dedicated to demystifying these occurrences. To read all of the blogs in this series, go here.

To kick off our series on demystifying and understanding email bounce backs and errors, we thought it would benefit everyone to go over how to read a bounce back. Some bounce backs are very cryptic and full of codes and numbers. How are you supposed to figure it out? Let’s break down a typical bounce back:

  1. The top part of this message is the actual bounce back. This is the “meat” of what you need to identify.  Sometimes bounces include lots of numbers and codes; ignore all that and find the string that references the 400 or 500 number.  (What’s the difference between a 400 and a 500 error?).  In this case the error is ‘550 No such user’. Since this account doesn’t exist at mxtoolbox.com the message was bounced by the recipient server.
  2. The second half of the bounce is the email headers. Keep in mind that not all bounce backs include this information, however, most do. This information is really helpful as it contains the Sender, Recipient, Date, Time and Subject, as well as server hops. If you are unable to figure out the issue, make sure you send the complete bounce back including the email headers to your IT administrator.  All of this information is critical in understanding a bounce back. If you need help reading headers, try our free tool, the Header Analyzer. It makes the email header a bit easier to read.

Microsoft Exchange
As with all things Exchange, they have their own way of doing things. Exchange bounces include a top header section; however, we tend to ignore that section as it has very little helpful information.  Remember to focus on the “Technical details” or the “Diagnostic Information for administrators;” as this is the “meat” of the data you need to analyze.   You may also notice that Exchange bounces include two conflicting “who rejected your message” statements. The second one labeled “Generating Server” is generally the server that issued the bounce.

Remember that knowledge is power!  We at MxToolBox are constantly educating ourselves about all the different bounce backs that exist.  Also keep in mind that with some Vendors and ISPs you have the ability to create custom bounce back errors…so you always have to be on your toes!

If this is a bit overwhelming or you don’t want to mess with understanding bounce backs or error codes, don’t worry.  It can take years of experience to feel comfortable reading and deciphering this information. We understand that you just want your email to work!  Implementing one of our Managed Business Email Products such as Spam and Virus Filtering or Hosted Email can help alleviate these issues and put someone in your back pocket to help understand when these problems occur.

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