Some B2B websites require e-mail validation at each login as a way to confirm that the user’s organizational affiliation remains valid.

Being able to read mail sent to an @example.com address doesn’t prove someone is an employee of Example Co., of course, but the inability to read such mail suggests that the user’s affiliation may have ended and that access granted by virtue of it should be blocked, at least for the time being.

Single sign-on is usually a better method for this, but it’s not always practicable to set up.