Disable alert e-mails from Mail / Calendar
It is indeed Mac Calendar problem as author of the question suggested. 

I faced the same issue and observed that I get these nasty "Alert - ..." emails only when Mac wakes up. I also did not get them before I started using my Mac.

To solve the problem on macOS 10.12.3:


Open Calendar app
Find your Google calendar on the list and right mouse click it
Select "Get Info" option from the context menu
Mark "Ignore alerts" checkbox in the popup window (see screenshot).