Imap on outlook 2013+ xlist / enhanced list

Dear vmin Support,

We are currently having a issue with IMAP and Outlook 2013/2016. It appears that non-native clients have a problem with the special folders. The following occurs When an IMAP account is configured Outlook requests (via XLIST or LIST-ENHANCED) which folders need to be set for Sent Items, Trash, Spam and concepts. Outlook doesn't appear to detect the correct folders and creates them. These new folders aren't marked as special folders. (see attachment)

If a client then sends a mail from concepts Outlook will not change the folder the mail is stored in (concepts --> sent) but just retains it in concepts. Also the button to empty the trash folder doesn't work.

We’ve now added xlist to our dovecot, but this doesn’t appear to fix the issue. Mail now randomly gets retained in concepts. We are running on:

Webmin version 1.840 Vmin version 5.07 Dovecot version 2.2.22

We would very much like to resolve this for our customers, but we seem to have hit a wall with this. If you need any further information, please do not hesitate to contact us.

Evert