I have a client who owns 4 companies. He has a different email address for each company.
One company uses Office 365 for email, the other 3 are POP accounts to a local ISP mail service. (firstname.lastname@example.org... email@example.com etc)
He also has an IPhone that he syncs with his Outlook calendar at each office. This results in numerous duplicate entries. It also results in 4 calendars in OWA, each with different appointments.
I need to fix this so his assistants in each office can all see and edit the same calendar. And that calendar to sync with his IPhone.
I am thinking about sharing his Office365 calendar to users in the other 3 companies. But not sure if they will be able to edit it (since they're not on Office365 and have a couple different versions of Outlook).