It's possible to have read only access to Outlook Calendars from Thunderbird. But you couldn't accept event invites or create new events. At least at my previous work, which I left last summer.
I apparently don't get event invites from Outlook Calendars then. All the invites that I get in Thunderbird from colleagues (on Thunderbird) and customer (no idea what they use) seem to work fine. Does Outlook not use the caldav standard that everyone else uses? Which clients do work with that then, only Outlook itself? Gotta be annoying if anyone in the company uses, say, an Android or iOS device
What I mean is that if you have an Outlook account, and you want to use Thunderbird for it, you will need to sync your Outlook calendar with Thunderbird. Outlook uses Exchange ActiveSync instead of CalDav/CardDav for this syncing.
The way to give Thunderbird these capabilities are by installing these two connected addons [1, 2]. At least till June 2022, I could see meeting invites from colleagues in Thunderbird. I would also see the translucent event in the calendar in Thunderbird. But accepting the invite would not work [2]. Also creating and sending Outlook calendar events from within Thunderbird didn't work. So, I always had to open the web Calendar to do these things. Thunderbird was only good for meeting reminders.
There is a new major release of the addon since then, so it is possible that the bug is fixed.
> I apparently don't get event invites from Outlook Calendars then
Obviously if your email/calendar account is something else, then you have no problem. If someone sends an invite to my gmail, from their outlook, I can accept it fine from within Thunderbird, because Thunderbird/gmail are communicating using Caldav (I think).
> Which clients do work with that then, only Outlook itself?
I will use Thunderbird as much as possible till it is pried from my cold dead hands!
Design improvement and responsiveness is good, think.
What I would like on the backend is for them to fix the maildir storage [1]. Currently email is stored in mbox, which is very buggy and causes all sorts of weird errors.
Alas, seamless synchronization with calendars and contacts managed by others is really hard -- and boring.
Improving design and responsiveness is so much easier -- and much more exciting!
So, all the development effort has gone into... improving design and responsiveness.