osTicket/osTicket-1.8 — pull request #129 by greezybacon (2013-11-12 15:59:21+00:00)
Title: Forbid update of email address to one of another user

Ultimately, in the user information ("contact information") form, forbid updating a user's email address to an email address in use by another user. Because email addresses are a unique identifier of user accounts, they cannot be reused between different users.