Outlook/Exchange vs. macOS calendaring

Question

Asked on Ask Different (apple.stackexchange.com) but no replies and only a few views. Maybe the wrong Venue? Maybe {tl:dr}? I apologize for being verbose but hope this helps me down the path of making things better for the assistants and executives.

We have several assistants that receive meeting invites for their executives. They are using Macs running Yosemite, El Capitan and Sierra with iCal and Apple Mail on hosted Exchange. We are looking to convert them to Outlook, replace ancient Office 2008 and upgrade them all to Sierra.

Currently they use iCloud calendars and the execs all subscribe to the assistant's iCloud account. Each has their own calendar under the assistant, but when one exec has a reminder, they all see it and it can be confusing.

They are explaining some odd behavior, such as when accepting an evite from someone on the outside (who doesn't know all the assistants), sometimes others are "automatically" added on some kind of forwarded response. Since this is all Apple stuff, I have no idea how it's working. In Outlook, you can forward, reply, accept, decline, etc. Why Apple Mail would take an accepted invitation and then send that on to others in the organization baffles me. Might be some iCloud settings?

When they were on POP/IMAP, when receiving an invitation, they could accept it and it would remain in their inbox (or so I'm told). Now it disappears, either into the trash, or completely (the completely I can recover out of deleted items via the hosted Exchange OWA page and put it back in the trash or inbox). Unsure why the behavior is inconsistent.

With their iCloud calendar, when an assistant accepts an appointment sent to her, she can choose which of her iCloud calendars it will appear on.

If I add Exchange calendar, although their iCloud calendar is default, the appointments still go to their Exchange calendar. So it's going to be all or nothing, no transition.

I can add the assistant as a delegate, but they cannot accept an appointment on behalf of their exec from her own inbox. She would have to send the appointment to the exec, then go into the exec's inbox and accept it which is clumsy.

So, if the assistant accepts something, perhaps she can forward it and we can do this with a rule to auto-accept anything from specific people: https://blogs.technet.microsoft.com/sharepoint_republic/2011/12/09/outlook-rule-to-auto-accept-or-auto-decline-meeting-invites/ I don't know if scripting is possible on OS X though.

Since Outlook (maybe it's addressed in 2016) on OS X cannot be set to retain accepted invites, this might work: https://apple.stackexchange.com/questions/142503/prevent-outlook-meeting-requests-from-auto-deleting

Any insight or recommendations are greatly appreciated!