Can I count on mail to a bad address bouncing back?

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Summary: If you send email to an invalid address or a closed account, usually you'll get a bounce back. Usually. The problem is that you cannot count on bounces.

Unfortunately, the answer is:

a) both

b) neither

and of course

c) all of the above.

Email bounce messages are both annoying and informative. They can help you fix a problem with an email you've sent, or they can simply be another message in a big pile of spam.

Unfortunately about the only thing you can count on is that you cannot count on bounce messages.

•

First, I have to ask, what does it mean for an account to be "closed"? It could mean:

• The user stopped using it. Email will still be successfully received, and simply accumulate. Nothing that would cause a bounce.

• The user could have "closed" the account, but the ISP hasn't released or actually deleted it yet. This is probably more common than you think, particularly with free email accounts. While the user thinks that things are closed and deleted, in reality all the ISP may have done is restricted his access until they get around to cleaning up "dead" accounts. Email may still be successfully received and accumulate until the cleanup happens.

• The account is actually closed. Here's where things get interesting.

With the ever-increasing influx of spam, many ISPs are choosing to ignore mail destined for invalid destinations. Why? To avoid flooding the internet with even more noise.

You've probably received bounce messages for email you didn't send. Spammers have "spoofed" the email such that it looks like it's coming from you and then blasted it out to anything they can find that looks like an email address. Some ISPs generate bounces if those addresses are invalid, and that's what you're seeing. Other ISPs don't generate bounces, since they're as bogus as the spam that caused them.

So, the bottom line here is that an ISP may, or may not, return a bounce on an invalid email address - or on any error, for that matter.

But it gets worse.

Because so many bounce messages are the result of spam, spam filters are now occasionally filtering them out as spam. So even if the recipient's email provider does send a bounce, there's actually no guarantee you'll get it!

Now, I will say this: most of the time bounces are generated and received and work pretty much as you expect. But the problem is that you can't count on it.

If you send an email to someone and don't get a bounce, that tells you nothing. They could have received the email, or not. There's actually no way to tell.

Related:

• Ask Leo! - Why does email bounce?

• Ask Leo! - Someone's sending from my email address! How do I stop them?!

• Ask Leo! - I keep getting bounce emails for addresses on my domain that don't exist. How can I stop this?

Article C2870 - December 13, 2006