Trouble with Outlook

I only use Outlook to add items to my partner's calendar. I can usually read things he sends through his Outlook on my regular email File, calendar, etc. Lately, however, anything he sends me from outlook through my Apple email is garbled. When I go to my Outlook to respond to a calendar invitation, it will load the invitation but not reply. He can reply to invitations I initiate from Outlook.

When he sends me information from his office computer, I can only read it if I use my account from our mutual employer (he is full time, I'm not).

I am trying to figure out if this trouble originated with the latest Apple security update, or if it is something coming from his workplace.

Any help would be appreciated....