Outlook vs. Cyrus

Dear colleagues,

please what is your experience regarding cyrus and outlook (2016/365)?
We notice problems especially with users that have large and bushy 
mailboxes - >10 GB, >100 subfolders.

Specifically:

- sync gets stuck - one (sent) mail cannot be synced from outlook to 
cyrus, and that stops any further receiving and sending of mail. I was 
able to identify the problematic mail using communication dump 
(/var/lib/cyrus/log/username/) and after deleting it from outlook, sync 
recovered.

- other times deleting OST file and resyncing it from imap helped

- user with two mailboxes on the same server - one mailbox stopped being 
checked for new mail until outlook/computer was restarted. The other 
mailbox was checked all the time. Perhaps IDLE could help, but we were 
unable to find where to enable it in outlook.

- flaky search, AFAIK Outlook searches only using it's local cache, 
ignoring any search/squatter capabilities on the server.

- moving mail from one folder to another says "item cannot be moved, 
because the message was modified". After clicking on other mail and back 
it can be moved just fine.

And maybe other similar problems usually solved by restarting outlook, 
computer, deleting ost, or creating new clean outlook profile and 
starting over.

Have others found similar issues regarding outlook + cyrus (or any other 
imap server)?

Have you found some tweaks that could improve how outlook and cyrus 
cooperate?

Our imapd.conf extract:

altnamespace: no
unixhierarchysep: no
hashimapspool: true
search_engine: squat
delete_mode: immediate
expunge_mode: default

We are running cyrus 3.0.8 (debian 10), and considering upgrading to 
3.2.6 (deb 11) or 3.4.2 (deb 11 + backports), or migrating to dovecot.

Do you have any experience if oulook works better newer versions of 
cyrus, or some other IMAP servers?


-- 
Best regards
         Vladislav Kurz


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