Vpopmail

From Qmail Info Wiki

Vpopmail (http://inter7.com/index.php?page=vpopmail) is a software package that adds virtual user@domain functionality to a standard qmail server. Simply put, it allows you to have bob@domain1.com and bob@domain2.com on your server without interfering with each other. Instead of using system accounts and /etc/passwd, vpopmail has its own authentication system