Review for ExQuilla for Exchange by educ
Rated 5 out of 5 stars
I've been using ExQuilla for some time and now I just tested it with the new Thunderbird 91. Setup and basic functionality are working fine. I can send/receive Emails without problems, so far so good.
I don't see any problems in paying a small annual fee, the developers are indeed working to maintain the addon for every new version of Thunderbird.
To create your own collections, you must have a Mozilla Add-ons account.