The mailbox in the message is the mailbox at your ISP, not the one in Outlook. So this seems a problem that should be solved at your ISP's. Contact their helpdesk. They can easily check it by sending a test message to you from their own account, just like you did yourself.
I don't think there's anything you can do about this yourself.
Kees
Friends sending me e-mail get this message every time they send me mail:
Permanent Failure: 550_Requested_action_not_taken:_mailbox_unavailable
Here's what's weird. Using Outlook 2003, I receive ALL their mail. To check this, I sent myself mail. Sure enough, I got my mail, but a few minutes later, I got the same error message in my inbox. When I go to my ISP's e-mail page and send myself mail, the same thing happens.
I have no problems sending and receiving, but people sending me mail recieve that error message and think their mail did not get to me.
POP3 setup correctly
XP-SP2
Office 2003>Outlook 2003

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