When will Hotmail return an undeliverable message?

One of the casualties in the war on spam is the "message
undeliverable" message that you might get back in response to an email
that ... well ... couldn't be delivered.

I say casualty, because you simply can't count on it any more.

I'll look at your specific scenario and then I'll delve into why you
can't count on bounce messages any more.

Most free email providers, Hotmail included, will eventually delete
accounts that haven't been used in "a while". Exactly how they treat
email sent to that account would depend on just where in that "while"
they are.

• Within 'X' days of the last login or use: the
  account remains active. X might be as little as 30 days, or much, much
  more. It might also change as mail services adjust their capacity to
  meet demand.

• After 'X' days but before 'Y' days after the last
  login or use: the account is "suspended" for inactivity. Typically, that
  means the contents of the account - all email and address book entries
  - are permanently deleted, but the account can still be recovered by
  logging in. The data would be lost, but the account would still be
  yours. For example, after 30 days of inactivity your messages and
  contacts would be deleted, but you might still have another 90 days to
  get the account and email address back. (Note: I'm making these numbers
  up!)

• After 'Y' days but before 'Z' days after the last
  login or use: the account is deleted. At this point it cannot be
  recovered.

• After 'Z' days after the last login or use: the
  account name is returned to the pool of available account names. A new
  account can be opened using the original, expired, account name. Note
  that this is not a reopen of the old account, this is a
  completely new account with no relationship to the old, other
  than the account name and/or email address.

As I mentioned, 'X', 'Y' and 'Z' are numbers that are determined by the
specific email provider, and could be short or long, and could change without
notice.

Now, your question boils down to where, in that process, do they
start sending bounce messages?

As long as the account is active, there should be no bounces.

While the account is "suspended" for inactivity, there's no way to
know. It's up to the email provider and they typically don't detail
whether they do or not. I would hope that if email is not going to be
delivered into the account's inbox that it would be rejected with a
bounce, but as we'll see in a moment, that's not always the case.

After the account is deleted, once again I would hope that
it would be rejected with a bounce, but it might not be.

As you can see - the answer boils down to "maybe, maybe not".

So why are bounce messages so unreliable? Why can't you count on
them?

Ultimately, we get to blame spam.

Bounce messages are often not sent at all, to prevent spam, and
bounce messages are often filtered as spam.

•

Spammers send a ton of email to email addresses that don't actually
exist. They just start "guessing" email addresses made up of likely
names and words and whatnot, and if even a tiny fraction are real email
addresses the fact that the vast majority go nowhere makes no
difference to the spammer. It costs them nothing to send email to bad
addresses, and the few that end up being real make up for it.

So, imagine that you're a large email service like Hotmail or GMail
or Yahoo, and you're getting millions and millions and
millions of emails every day to accounts that don't exist. The
vast majority are from spammers, while only a very few are from people
who've perhaps mistyped an email address. Do you respond by flooding
the internet with millions and millions of bounce messages that,
themselves, may go nowhere?

Probably not.

Hence, some of those legitimate mistakes will also result in no
bounce message. At all. Those emails just disappear.

There's another approach that spammers use as well that actually
uses bounce messages to get their message sent.

A spammer might send an email to "foo@example.com", but also spoof
the "From:" address to be "bar@example.com". That means that if "foo"
rejects the message with a bounce "bar" will get the bounce
message.

Remember that the goal of a spammer is to get a real person to
actually read their message. If you get a bounce message, don't you
look at what it was that failed in case it was a message you intended
to get out? If that's a 'fake' bounce, then the spammer just got you to
look at his message.

And by now we've all gotten bounce messages to email we didn't
send.

Spam filters are aware of this technique, and as a result are
looking at bounce messages that much more closely. The bottom line is
that legitimate bounce messages might well be getting filtered along
with spam.

•

If you send an email and get no reply - no reply from the recipient
and no bounce message from the email system - that tells you exactly
nothing. It may have been delivered and read, it may have been lost
completely; there's no way to know.

You can no longer count on a bounce message to tell you that there's
been a failure. The failure may occur quite silently.