vpopmail

If you're looking to automate the setup and maintenance of virtual domain email configurations for qmail, vpopmail (vchkpw) is the software for you. This collection of programs and libraries supports a single UID/GID or any valid UID/GID in /etc/passwd with a home directory, and also provides features for other applications that need to maintain virtual domain email accounts.

vpopmail supports both named or IP-based domains and can easily integrate with various applications such as vqadmin, qmailadmin, vqregister, sqwebmail, and courier-imap. It's highly flexible and supports various authentication methods including MySQL, Sybase, Oracle, LDAP, and file-based authentication.

One of its notable features is its support for SMTP authentication combined with the qmail-smtp-auth patch. Additionally, it allows for user quotas and roaming users, letting users SMTP relay after POP authentication.

Overall, if you're looking for a versatile and reliable tool for managing virtual domain email configurations in your qmail installations, vpopmail is definitely worth considering.