VPopMail is an open-source
GPLsoftware package used for managing virtual
e-mail domains and non-password e-mail accounts on
e-mailservers. It was originally developed by Inter7.[1]
Features
Support for 1 to 23 million virtual e-mail domains using a "grow as it goes" balanced directory tree
Support for 1 to 23 million e-mail users per domain using the same balanced tree structure
Automating e-mail configurations into command line programs that can be used for scripts and documented API library calls
Automating Unix user/group/other permissions of directories and files
Authenticated relay control of e-mail SMTP servers