Virtual Users And Domains With Postfix, Courier, MySQL And SquirrelMail (CentOS 6.2 x86_64) | HowtoForge – Linux Howtos and Tutorials Virtual Users And Domains With Postfix, Courier, MySQL And SquirrelMail (CentOS 6.2 x86_64) | HowtoForge – Linux Howtos and Tutorials.