The original problem seems to be resolved. I have not had any e-mails sent when I snooze or dismiss meetings. That's the good news. (great news)
I am seeing 2 new odd behaviors. However, they are not deal breakers for me. I'll stick with Mail.app and Calendar.app for now. Those issue are:
When changing a single instance of a reoccurring meeting, 3 calendar notifications are sent. In my case, most of my reoccurring meetings are on custom schedules. (IE: 3 Wednesday of each month) This may be related. So, in the example case, if I move the next meeting to the Tuesday before, 3 notifications are sent. My theory is that this is due to the custom schedule and the three notifications are:
- Change to orginal meeting series
- Delete the Wednesday meeting
- Creation of new Tuesday meeting
The other issue is with Hotmail. (I have multiple account synced with Mail.app.) Each time I send a mail with Hotmail, 2 are sent. I've tested this and verified on 2 different Macs. Both are running 10.10.5 and this issue did not happen in previous versions.
Again, these are not deal breakers for me and I'll deal with these instead of going back to Outlook.