Using Multiple email domains as one organizaiont

Question

The challenge:
Multiple independent email accounts with different domains need to function as one large company.
john@123.com, frank@jaswant .com, wendy@1x2.com need to function as if they were one company.
Need to replicate email, calendar, teams functionality that exists under one domain, under an exchange server, and provide for calendar visibility, broadcast messaging, fully unified capabilities.
All need to be managed by a single administrative entity.
The individual email domains need to stay intact... being that the users keep their existing domain as their functioning email address.
Can't use sub-domains from the perspective that the visible email address must stay the same. Can't go from john@123.com to john@123.corp.com.

Question
Is this scenario even possible?
If yes... then how?

Any information is appreciated.