You may encounter the following error message with Microsoft Outlook, while browsing your IMAP tree folders, sending a message or moving message across them :
IMAP server wants to alert you to the following: fatal error: no such file or directory
I have observed this behaviour with a mailbox and a Linux mail servers (Qmail, Postfix, Exim) running “courier-imap”. The reason seem to be related to the folder index file (courierimapsubscribed), which does not have the full folder index any more.
To resolve this matter, do the following :
1. Make sure that the affected user that is experiencing the issue does not have any mail client opened anywhere
2. On the IMAP/mail server, browse to the user mailbox
3. Locate the folder index file named “courierimapsubscribed”
4. Move the courierimapsubscribed file as courierimapsubscribed.old
5. Open the mail client again, the index will be regenerated (it may take a little while on large mailbox).