IMAP folders showing no messages in Office 365 Outlook

[Andrew Bernard via dovecot]

I'm new to Dovecot. Using Dovecot IMAP with Postfix, everything works 
fine using Thunderbird. But with the same setup, no messages show in 
IMAP folders for user accounts created in Outlook, accessing exactly the 
same server as the accounts in Thunderbird.

Dovecot version 2.3.7.1.
Is there any configuration required that is special to support Office 
365 Outlook clients? How to debug this?

Andrew