Outlook and return options to LSUB

A while back, users started to experience issues with IMAP LIST Extension for Special-Use Mailboxes. This to a level where a decision was made to temporarily suspend supporting Special-Use at Kolab Now.

Lately we have found ways to get around the problems that were present back then, and over the change of the year we introduced an update that, among other great improvements, contained these solutions and re-enabled the Special-Use.

Unfortunately, meanwhile Microsoft has also updated Outlook, and their update has changed the return options that Outlook is using with the LSUB command on the IMAP server.

This has caused issues for some users, who connect Outlook to Kolab Now via IMAP. Those users are suddenly not able to see some of their folders and mails in Outlook. The folders are perfectly visible in the web client and in other IMAP clients like mobile clients, Mac Mail and Thunderbird.

While the RFC compliance issue (the LSUB command does not accept a client specifying RETURN options) certainly has been made visible by Microsoft changing the behavior of Outlook, inversely Kolab Now providing an update to the benefit of all other clients has suddenly shown the related Outlook behavior to be faulty.

The root cause of the issue can be narrowed down to the expectations from Cyrus IMAP while parsing the LSUB command. Besides filing an upstream ticket, Kolab Systems has engaged in this issue and is contributing a fix to the Cyrus IMAP code. This fix is now going through test and QA, and should be ready to be deployed to Kolab Now soon.

If you are one of the users, who has problems because you are connecting Outlook to Kolab Now via IMAP, then you can work around the issue by – either using another IMAP client – or by connecting your Outlook to Kolab Now via ActiveSync, until the fix for Cyrus IMAP is ready and deployed.

If you have any questions or concerns in this context, then please contact support@kolabnow.com.