Managing a mail system with virtual users is annoying. The authoritative database of users is stored in one table, but every other piece of software keeps its own database of users. If you're using PostfixAdmin to manage your users, what happens when you delete a user? Chances are, nothing happens: mail directories are left behind, webmail preferences are saved, address books become orphaned. That's what mailshears was designed to fix. It cleans up after you remove a user or domain. Another stupidly difficult task is renaming a single email account. It's easy to move the user in one database, but then all of the remaining filesystem directories and databases need to be updated as well. Since these two tasks are related, mailshears does them both.