We have a number of users who do not have an email address associated with our domain name, and there is no need for them to be given an email address that is associated. On MSP Mail a user could log in using their primary exchange address rather than the primary domain address. For example, primary domain is test.com and a lot of people also have an email address of email@example.com, but we also have other users who work on the test.com domain, but work for a different registered company, and therefore have a different email address, for example firstname.lastname@example.org.
Idea No. 3157