Ask Leo: Why Does Email Bounce?


By Leo Notenboom

Sometimes my email bounces. Every so often I’ll send a message,
and a short time later I’ll receive a reply saying that the email failed to go
through. Why does it happen? And how do I fix it?

Well, I’m afraid that there are many reasons mail could bounce. In
fact there are so many ways it could fail that sometimes I’m amazed that it
works at all. But it definitely works most of the time, and one of the ways it
works is that very bounce message you get.

You see, there’s gold in that bounce message. It’s not only telling you that
your message didn’t go through, but if you look a little closer, you’ll see
it’s trying to tell you why.

Bounce messages can vary in format and in exact wording, depending on the
mail server that’s sending the message back to you. Different types of mail
servers use different terminology. Some are quite geeky and difficult to
understand. Others seem to take five paragraphs to tell you that you probably
just mistyped the email address you were sending to.

What I’ll do here is list some of the most common messages, what they mean,
and what you can do. Remember, though – a message you get may not be worded
exactly as I list it here. You’ll have to look carefully at the bounce
message you receive and see which of these it’s most like.

Examining a Bounce

First, let’s look at a couple of bounce messages. Buried in the all the
geekery, I’ve highlighted a couple of important things:

   ----- The following addresses had permanent fatal errors -----
    (reason: 553 sorry, relaying denied from your location [] (#5.7.1))
   ----- Transcript of session follows -----
... while talking to
>>>> DATA
<<< 553 sorry, relaying denied from your location [] (#5.7.1)
550 5.1.1 <>... User unknown 
<<< 503 RCPT first (#5.5.1)

Here’s a bounce from another mail server which attempts to be more

Hi. This is the qmail-send program at
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.
<>: does not like recipient.
Remote host said: 550 MAILBOX NOT FOUND 
Giving up on

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1 thought on “Ask Leo: Why Does Email Bounce?”

  1. I have a question for you. The last three or four times I emailed a good friend from Florida. The address bounces back in reverse. To me from him as the subject. But there is no email message. Does he have me blocked for some reason or another? Or is there just a problem somewhere. This bounce seems almost instantaniously. I appreciate any help or answer you can give me in this matter.

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