That's massive. So many of us that have used Gmail (well G Suite, Google Workplace, and the previous branding names), would certainly love to have an Apple solution.
Unfortunately a perfect solution is difficult to find.
.
Google gives you a lot of Admin Power (you can even do DKIM on your own domain) - but you may not trust them
with your data and the other services are not well integrated into the Apple World. It is also not that cheap.
.
Microsoft has not a bad offering for e.g. a family (as you get Office with that).
Outlook.com has minimalistic custom domain support - BUT they do not accept all Email: They randomly block servers
and you are never sure you get all the Email you should.
If you get the more expensive Exchange.Online: that is a real pro-offering and gives you full control - nothing to say
against it, except that it is costly and requires some skills.
.
Apple is trustworthy and certainly well integrated into the Apple Ecosystem. I would be skeptical however that
they provide the required Admin Tools - I fear this will be a very "consumer oriented" implementation that
keeps the power users unsatisfied-
.
Roll-your-own: With e.g. mailcow and a custom server this has a lot of advantages (I am running this and I can do
DMARC, DKIM, DANE, SPF whatever I like). Problem is - the big providers tend to block the small servers (specially
Microsoft) and that mostly kills that option. What is the value of a mailserver, if you cannot send to everyone?
Currently I stay with "roll-your-own" but a decent Apple offering would make me switch in a jiffy. Let's wait and see!