Vpopmail

VPopMail is an open-source GPL software package used for managing virtual e-mail domains and non-password e-mail accounts on e-mail servers. It was originally developed by Inter 7.

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
 * Supports name or IP-based virtual domains
 * Configurable logging
 * Support for MySQL, Oracle, PostgreSQL, /etc/passwd, /etc/shadow, LDAP, Sybase, and default CDB authentication storage
 * Delivers directly to Maildir for use with qmail-pop3d, .qmail files or any other Maildir program
 * Unique domains for each directory under vpopmail user with a Unique password files for each domain
 * Documented command line programs that can be used in scripts or for remote admin
 * Documented C library for vpopmail features and transactions
 * Daemon that manages mail accounts via TCP/IP control port

Operating system requirements
The minimum operating system requirement for vpopmail is
 * FreeBSD
 * Linux
 * NetBSD
 * OpenBSD
 * Solaris
 * Tru64
 * HP-UX
 * UnixWare