I can’t say which of these might be the cause in your situation. So whatever might cause a “mailbox unavailable” on one system might generate a completely different message from another.Īll we can do is make some guesses. Unless there’s additional text in the error message saying more - which there typically isn’t - there’s just no way to know exactly why it failed.ĭifferent mail systems use different error texts to report the same errors. The only thing it tells you is that the mail could not be delivered. “Mailbox unavailable” is a frustratingly vague message. The “mailbox unavailable” error is the email equivalent of saying, “Something didn’t work”. Unless there’s more information included with the message, there’s rarely any way to get more details. “Mailbox unavailable” can indicate that your email message failed to deliver for any number of different reasons, ranging from bad email addresses to closed or suspended accounts to quotas having been reached to mail server problems and more.
