[finales]

As a former MSFT employee (on Azure), Teams daily active users are counted even when someone on Outlook hosts a meeting, which is automatically converted into a Teams meeting link. Therefore, unless an enterprise is still sticking with Skype, Teams users will automatically get trickled in from Outlook.

[elygre]

That would only be if they hosted an online meeting (an audio or video conference), not for any outlook meeting (i.e. a meeting booked with outlook doing scheduling, but meeting happening in a good old meeting room). And that is then comparable to slack video conferencing, so probably a fair comparison.