So you’ve got yourself one of those dreaded Microsoft Outlook errors? Same here:
Task ‘Checking for new mail in subscribed folders on Mail Failure Logs.’ reported error (0×8004DF0B) : ‘Outlook is unable to download folder (null) from the IMAP e-mail server for account Mail Failure Logs. Error: The connection to the server is unavailable. Outlook must be online or connected to complete this action. If you continue to receive this message, contact your server administrator or Internet service provider (ISP).’
Truth be told, Bill Gates isn’t at fault here. This is actually a courier-imap setting. To correct the issue, shell to your server, and edit /etc/courier-imap/imapd (may be located elsewhere on your *nix distro) look for the following flag: MAXPERIP=4, increase the number and restar the courier services. The error is no longer there.