Bounce Codes: Understanding Why Email Bounces Back

All email list administrators know what they look like, but what do they mean? Some bounces seem to have a clear meaning, but others are cryptic enough to make any normal person tear their hair out. The way bounce codes look when they show up is not even consistent!

Sometimes they'll look like this:

Remote-MTA: dns; smtp.myemail.com [192.0.2.3]

Diagnostic-Code: smtp; 550 No such user here

Other times you'll see something like this:

while talking to smtp.store.example [192.0.2.3]

>>> RCPT TO:<This email address is being protected from spambots. You need JavaScript enabled to view it.>

<<< 550 No such user here

Okay. Take a step back, a deep breath and relax.

You can safely ignore most of what you see in both messages. The important part of the message is the 3 digit numerical code, 550 and the short description that follows immediately.

What do those three digit bounce codes mean? Well here's a list of the codes that matter to a mailing list manager and what they are supposed to mean:

• 550 - The requested command failed because the user’s mailbox was unavailable (such as not found)
• 551 - The recipient is not local to the server.
• 552 - The action was aborted due to exceeded storage allocation.
• 553 - The command was aborted because the mailbox name is invalid.
• 554 - The transaction failed for some unstated reason.

The code to worry about for email marketers is code 550. Usually this means that there is no mailbox for that address. At this point you would want to cull the address from your list to avoid wasting resources on mailings, but even a code 552 which means that the user has exceeded their storage allocation is important. If the mailbox is full for several mailings it might be best to remove the address from the list.

Bounce codes are a great tool for refining lists gor maximum efficiency. If you have any questions about bounce codes or about how we can help you manage your email marketing please contact us.