I set up a google sites site.
I added some people to administrate it.
I notice that one guy whose email address is his own domain like tim@blob.com it lets me add his email address.
Another person that's gary@hotmail.com it lets me add him
But then when I try to add sarah@msn.com it says "Sorry, you cannot share with sarah@msn.com because they do not have a Google Account."
Well, how does it know whether tim@blob.com has a google account. And why does it have no problem with gary@hotmail.com?!
Best Answer
When creating a Google account, one can use a non-google email address.
If a person's non-google domain email address could be added to administrate a google sites site, it was because they created a google account with that email address.