OutLook support

[Deborah Pickett]

On 2020-09-04 18.30, Andrea Venturoli wrote:
> What's the status of interoperability today?
> Will OL 2013 work reliably with CyrusIMAP 3.0? 3.2?
> What about newer versions of OL? 

Hi Andrea,

I can offer anecdata of interoperability between Cyrus 3.0.x and Outlook 
2016 from ten months of experience.

Like Outlook in general, it works fine, until it doesn't. With ~40 users 
with mailboxes up to 15 GB in size, I've had to help users start with 
fresh Outlook profiles about half a dozen times when their Outlook data 
file got corrupted.

Some specific observations:

Like any IMAP account in Outlook, you lose the ability to tag messages 
with colour.  All you can do is flag or unflag a message.

Outlook does not handle the \Deleted flag well, and it has a habit of 
showing messages which are \Deleted as if they are still present 
(especially in Drafts). I recommend configuring all clients sharing an 
account with Outlook to purge folders early and often.

Outlook respects special-use folders about as well as other IMAP 
clients, which is to say, not super-well.  If you try to change which 
folder is the Trash folder using cyradm, Outlook may not notice the 
change.  That said, it's not as bad as Windows 10 mail, which flat out 
refuses to respect special-use folder tags at all.

64-bit Outlook is needed if both (a) your data file is > 2 GB, and (b) 
you want search indexing to work.  With 32-bit Outlook, search will 
silently miss messages.

Outlook is inefficient at IMAP synchronization.  If you have large 
mailboxes, it can spend a lot of its time synchronizing subscribed 
folders.  There are ways of winnowing the list of folders that Outlook 
tries to sync during Send And Receive, and this helps a bit.

Outlook by default wants to send read receipts.  These invisible 
messages can silently clog up the outbox, preventing any messages from 
being sent.  It is a very good idea to disable sending read receipts 
entirely; I have set a Group Policy object to do this. I've had to use a 
free program called MFCMAPI to manually delete queued read receipts that 
accidentally got through.

To sync Outlook with Cyrus contacts, calendars and tasks, the free 
Outlook CalDav Synchronizer add-in works well (but sync rules are 
tedious to set up, and I haven't found a way to deploy preconfigured 
sync rules to users).  Outlook tries to disable the add-in because it 
slows down startup, but you can prevent this with a registry setting.

Rarely, Outlook will decide that a folder is local-only, and any 
messages moved into that folder will stop syncing with Cyrus.  The only 
fix I have found is to create a new Outlook profile (and then hunt for 
lost messages to drag back under synchronized folders).

Renaming a folder, or moving it somewhere else, in Outlook usually 
works.  Rarely, it'll make the folder local-only.  A slightly more 
robust way of renaming a folder is to make a new folder with the new 
name, and move the contents of the old folder over to the new folder.  I 
have seen this fail too.

These corruptions seem to occur more often in "Other Users" and "Shared 
Folders", but this might just be because said folders are huge (> 4 GB) 
in my company.

Of course, it's unlikely that any of these irritations will ever get 
fixed by Microsoft.  In the long term, I am considering migrating my 
users from Outlook to Thunderbird or webmail.

Hope these data points are useful.

Deborah