We have business partners in many external agencies, which each have several users who need access to our portal. All these people have existing business email addresses -- some are on Exchange, others use Gmail, etc.; they are not interested in creating a Microsoft account and checking a Microsoft email solely in the context of our portal.
We want to be able to create a new portal user, specify an existing, non-Microsoft email address, and that will be the user's login and primary email.
I can't figure out how to do this, and it's starting to look like it's not possible, but that seems absurd. Do all portal users have to maintain a separate Microsoft account and email address in order to use our secure portal?