vpopmail (vchkpw) is a collection of programs and a library to
automate the creation and maintenance of virtual domain email
configurations for qmail installations using either a single UID/GID
or any valid UID/GID in /etc/passwd with a home directory. Features
are provided in the library for other applications which need to
maintain virtual domain email accounts. It supports named or IP-based
domains. It works with vqadmin, qmailadmin, vqregister, sqwebmail, and
courier-imap. It supports MySQL, Sybase, Oracle, LDAP, and file-based
(DJB constant database) authentication. It supports SMTP
authentication combined with the qmail-smtp-auth patch. It supports
user quotas and roaming users (SMTP relay after POP authentication).