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Mailbox unavailable is a common message in returned email or "bounces" that actually says very little other than that the email could not be delivered.

What does "smtp; 550 Requested action not taken: mailbox unavailable mean?" I can no longer send emails to my friend at *****@live.com ... the mail comes back with this message.

Well, on one hand it means exactly what it says: your friend's mailbox isn't available, and your message could not be delivered.

In fact, that's exactly, and the only thing it's saying.

But we can make some guesses as to what it might mean.

"Mailbox unavailable" is a frustratingly vague message. Quite literally it's telling you that the mail could not be delivered, without giving you any clue as to why. None. Unless there's additional text in the error message saying more, there's simply no way to know exactly why it failed.

It gets worse. Different mail systems use different error texts to report the same errors. So whatever might cause a "mailbox unavailable" from one system, might well generate a completely different (and hopefully more useful) message from another.

So, all we can do is guess.

"'Mailbox unavailable' is a frustratingly vague message."

But, we can make some educated guesses.

First let me be clear: I'm NOT saying that any of these did happen. We don't know. These are simply possibilities, nothing more.

Of course, you should start by being absolutely positively certain that you have the email address exactly correct. Any error could have you sending to a non-existent account, which could easily result in this error.

If you are certain that your friend should still have his email account, then it's likely to be a temporary problem at his end. More often than not, it's something as simple as an account that has reached its quota and simply doesn't have room for any more mail. Your friend would have to download or delete email in his account to make room for new messages.

Some services use "Mailbox unavailable" as an error message to reject suspected spam. If your email somehow looks like spam, or your email address has somehow become associated with being a spammer, this could be the system rejecting your message.

It's possible that the server on which your friend receives email has been misconfigured, and is erroneously rejecting mail to him for a variety of reasons.

It's possible that your friends account was suspended or deleted for abuse. Sometimes this means that he was doing something he shouldn't have, but more often than not it means that his account was hacked or spoofed and taken over by someone who did. Once they got caught, the account might be closed or disabled.

Perhaps your friend closed his account without telling you. This happens, intentionally or by accident. You would need to find another way to contact your friend that doesn't involve this particular email account.

While those are all things to look at and rule out, what this all boils down to is that basically any reason for email not being delivered could, in fact, cause this message.

In your shoes - I would contact your friend via some other means.

Article C3738 - May 21, 2009 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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3 Comments
Mark Jacobs
May 22, 2009 7:05 AM

one more possibilty: your friend hasn't checked their email in 30 days or in some cases 90 therefore causing it to be suspended or closed to to inactivity. If this is the case it can sometimes be reactivated.

Brian M
May 26, 2009 10:10 AM

Another possibility is that the mail server is down temporarily. It doesn't happen often, but any server can fail due to DOS attack, takeover attempt, hardware issue, network issue, etc. My e-mail is with a smaller ISP and the mail server goes down for a few hours to a day about once every three years. I don't mind because they have great customer service - when you call you can get a real person who can actually tell you what is happening! [No standard responses like "your computer is not configured correctly" or "we'll get back to you" or "would you like to upgrade your service" or ....]

Dan
November 9, 2009 4:37 PM

Leo, I hope you can set me straight. I have been a MSN Explorer member for a few years now. All of a sudden a couple of months ago I am unable to get on my usual e-Mail program. I have tryied to ask for a CD to get back on line with them with NO avail. WHY????? Please tell me whats going on with MSN and when I can get back to my usual e-mail page. I have already downloaded to Explorer 8 and still I can't get to my e-mail page. If you can have a CD sent to me??

Thank You,

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