I was mortified by Cortana auto-extracting todos from private emails but my father in his late 50’s said it was neat and very useful for him. So it goes.
I don't trust them because I know that they're reporting to their real bosses, who aren't me. If I could have a personal assistant that was completely local and under my control, I'd begin to get interested in them.
When I see that several emails I have not opened are already on my calendar, I am less happy about it.
Sure, for many folks this will be fine. But it seems an unnecessary denial of service attack vector that needs more engineering to protect than makes sense.
That said, I'd also assume that full emails are not sent to my device until I open them, unless I setup something.