Nice short little “how to fix this” one.
I upgraded to Office 2013 and found that when Outlook connected to my local IMAP server it wanted to keep most of the “special” folders locally. This didn’t concern me too much, except for the “Sent Items” folder, which I really want to keep and share between desktop reinstalls or just between the three or four machines I read and send email from these days.
After a long piece of searching around all the different account and general options in Outlook I came to the conclusion that the manual configuration that used to be available in Outlook 2010 for choosing where each “special” folder would point to had just gone so I had to go on a bit of a hunt around Google to figure out where they’d gone!
Turns out, Outlook 2013 uses the XLIST command in IMAP to determine what each special folder is on the server and if it doesn’t find it there then it just makes “This computer only” folders to hold the information. Cyrus can be configured to properly report these (as you’d expect) and adding the following to my /etc/imapd.conf fixed the problem, after deleting my account in Outlook and recreating it:
# Special-Use Mailboxes. Use xlist- prefix to the list of special use
# attributes defined in RFC 6154. Attribute name in the configuration
# key should be defined in lowercase. The attribute value is case
# sensitive, may contain whitespace and and must be valid
# UTF7-IMAP string.
Now Outook behaves itself, stores all the sent items in “Sent”, the deleted items in “Trash” and drafts in “Drafts”. All my other devices (Android, iOS, etc.) seem to honor the settings as well.