Cannot see/accept/decline invitations from Exchange My wife and I send each other calendar invitations from time to time. She is on an Exchange account, while I am not. I have a variety of email accounts, including iCloud, Gmail, and non-iCloud, non-Gmail accounts.

When my wife sends me an invitation, regardless of which of my accounts she sends it to, it doesn't appear in the Calendar app on either my phone or my Macbook. Instead, it simply shows up in the Mail app as an email with a .ics attachment. I can't see anything about the invitation without opening the attachment. This is especially bad with updates and cancellations, as I can't see what has changed, and cancelled items never seem to get deleted from my calendar.

When I send her invitations, she has the same problems; invitations come through as attachments.

What could be causing this?

Note: we were both on the same Exchange server in the past, when we both worked at the same place, and had no problems sending, viewing, and accepting invitations on our phones and PCs. But we have had the problems above ever since I left that employer.
This is not a great answer, but it's a workaround for now. I set up an account on Outlook.com. Invitations to or from that address work seamlessly, so both my wife and I can open each other's invitations, accept, decline, etc.

The downside is that this only works for events on my Outlook.com calendar. There's still no way to accept an invitation from her and put it on my iCloud calendar, and she still gets an attachment if I send an invitation from iCloud or some other account. So, I very much consider this a workaround, not a solution, and would appreciate any actual answers.