I'm backing to using it at my new job (Office 365 subscription with all the desktop apps), and it's literally unusable for several minutes at startup. The UI just stops responding while it presumably does some background sync. I can't even click a button and start writing an email. Confirmed on two different computers.
This is the sort of characteristic I'd expect from a junior dev writing an Electron app in his spare time. I don't expect it from one of the three flagship apps of Microsoft Office.
My current flow has become launching Outlook to send an email, then realizing what's going to happen, open Notepad++ to write my emails in, then when Outlook finally becomes responsive again after a few minutes, I copy-paste them in it. Every time I do this, I think less of Microsoft.
When did this change happen? How does something like this pass QA? "Works for the QA guy on our 10Gbps LAN, therefore no problem"?
For me, it's the calendar that getting synced at each start and slowing everything down. It's not the emails / exchange.