qmail-ldap is an extension to stock qmail-1.03 to get all user account information from an LDAP database. Its primary target is POP toasters with thousands to millions of users, such as in ISP, FreeMail, and Corporate environments. It features full SMTP/POP3/IMAP server clustering for scaling and high availablity. Additionally there are state-of-the art spam filters, TLS SMTP encrytion, and mailbox quotas. A migration path for Netscape Messenger and Software.com's Post.Office installations is provided.
qmail-spp provides plug-in support for the qmail SMTP daemon (qmail-smtpd). It allows you to write external programs and use them to check SMTP command argument validity. The plug-in can trigger several actions, like denying a command with an error message, logging data, adding a header, and much more.
qpsmtpd is a flexible smtpd daemon written in Perl. Apart from the core SMTP features, all functionality is implemented in small "extension plugins" using the easy-to-use object oriented plugin API. qpsmtpd was originally written as a drop-in qmail-smtpd replacement, but now it also includes an smtp forward and a postfix "backend".
queue_repair can be used to check or correct most corruptions of the queue in qmail (resulting from filesystem damage, etc). Functionality includes automatic, dynamic determination of UIDs and GIDs. Automatic, dynamic determination of use of big-todo. Handles basic tasks like fixing a queue restored from backups, incorrect ownership or permissions of directories and files, missing or extra split subdirectories, unexpected files or other directories, or creating a valid queue from scratch.