Are you looking for free mail server which runs on Linux OS and have fancy admin and management tools? You can give a try to iRedMail. iRedMail is Open Source Mail Server Solution for RHEL/CentOS/Debian/Ubuntu/FreeBSD. iRedMail is a shell script that lets you quickly deploy a full-featured mail solution in less than 2 minutes. iRedMail supports both OpenLDAP and MySQL as backends for storing virtual domains and users. Click here for installation guide and enjoy in free software.