mac.com email server down?

The mac.com email server is not delivering messages, at least for some users. We have received numerous reports from users who are unable to receive mail. For example, Ken Simon writes:

"Many mac.com email addresses have been down for more than 12 hours now. A quick check of Apple's tech support forum shows that Apple has still not commented, despite many posts begging for status. One user recommended switching from POP to IMAP in the OS X Mail application, but this did not work for me. The server accepts my password, but simply doesn't find any mail, even though I know there are at least three messages that should have arrived."

There are also numerous similar messages posted on Apple's Discussion Board.