As the guy responsible for the email server at my company, I usually get tasked with troubleshooting all the Non-Delivery Reports (NDRs) for our end users. We call them "bounce messages" in our office because it appears that when you send the message - it bounces back.
What many users don't understand is that the reason the email bounced is usually right in the bounce message itself.
I always look for certain text in the bounce message:
Diagnostic information for administrators:
Generating server: servername.appriver.com
receivingdomain.com #<receivingdomain.com #5.0.0 smtp;message text rejected by receivingdomain.com.s8a1.psmtp.com:
552 5.3.4 Message size exceeds fixed maximum message size> #SMTP#
You want to look for the response of the server - that is your biggest clue. in the case above it's: "Message size exceeds fixed maximum message size" or in plain english - "I rejected your email because it's too big."
Here are more popular ones:
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.
I'm not going to go onto all the different errors because there is plenty of that info here on the web. The purpose of this post is to just show my train of thought when trying to figure out what's going on with a bounce. So here is my workflow.
Do we start to see the theme? My unscientific opinion is that around 90% of all NDRs are one of three things:
If mail is flowing to all other domains without an issue, but just one domain is bouncing or one email address in a domain - then it's NOT you. It's them.