Moving to “E-mail” based login is all the rage. Recently a large customer wanted to use the E-Mail as the login. A new User Principal Name (UPN) suffix was created so a UPN suffix that did not match the domain

How well does cross domain authentication work across a Trust? If you have a Forest trust, pretty good. Just make sure you have your UPN routing setup on the trust configuration. And across a domain trust? Not so well, and