To be fair exchange works quite well for mail and calendar, it syncs very fast, is easy to set up and the cloud version is easy to administer (i never had to admin an on-prem exchange but ive heard its not fun).
Using this infra for teams makes sense since it already works well. As one poster said, its probably via some hidden folder.
I wonder what they did with skype, did they actually integrate any of it into teams or just dump it entirely?
On-prem Exchange is usually fine. Migration is a pain, but for a mid-size org you can mostly just install it and use it. If you have multiple servers distributed globally and database availability groups and such, yeah, it gets to be its own thing, but that's because at that point you're huge and you're going to feel the pain no matter what platform you run.
Teams was built from Skype. The fundamental infra for communication (chat, video call) was pulled out of Skype as a separate component and integrated into both. Skype the client is completely sunset, but a part of its back-end will continue to be used.
Teams came from Skype. Skype Lync was just a client (so far as I know). Don't take my word for it though, I was not there during the transition, this is just my understanding from talking to the ones that were.
Using this infra for teams makes sense since it already works well. As one poster said, its probably via some hidden folder.
I wonder what they did with skype, did they actually integrate any of it into teams or just dump it entirely?