Unfortunately, the answer is:
- All of the above
Unfortunately, about the only thing you can count on is that you cannot count on bounce messages.
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What’s a bounce?
Just to be clear, “bounce” is the term we use when email we send causes an error message (also in the form of an email message) to return to us. Usually, though not always, the error message includes the original email.
The email you sent has not been delivered, and is thought of as having “bounced back” to you.
Hopefully, the error message contained in the bounce tells you why it bounced.
What is this “closed” you speak of?
I have to ask what you mean by a “closed” account in your question. It could mean many things, including:
- The user stopped using it. Email will be successfully received and accumulate. There’s nothing here that would cause a bounce.
- The user could have “closed” the account, but the ISP hasn’t released or deleted it yet. Email may still accumulate without bouncing until cleanup happens after some period of time.
- The account existed, but is now closed.
- The account no longer exists (or never did).
While you might think of some of those states as being “closed”, not all of them will cause a bounce, and none of them require a bounce.
With the ever-increasing influx of spam, many ISPs choose to ignore mail destined for invalid or closed 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 so 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.
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, even if a returning bounce message is the result of some email you actually did send, some spam filters now filter those bounces out as spam.
So even if the recipient’s email provider sends a bounce, there’s no guarantee you’ll get it!
Bounces usually happen, but…
Now, lest you give up all hope, I will say this: most of the time, bounces are generated and received and work pretty much as you expect. The problem is, 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.
You can only tell if they got it if they reply or somehow act on the information you included in the mail.
But if you hear and see nothing, you just can’t tell whether or not the email arrived. (And of course, you certainly can’t tell if they actually read it if it did. 🙂 )