getmail is intended as a simple, secure, and reliable replacement for fetchmail. It retrieves email (either all messages, or only unread messages) from one or more POP3, SPDS, or IMAP4 servers (with or without SSL) for one or more email accounts, and reliably delivers into qmail-style Maildirs, mboxrd files, or through external MDAs (command deliveries) specified on a per-account basis. getmail also has excellent support for domain (multidrop) mailboxes, including delivering messages to different users or destinations based on the envelope recipient address.
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).
Designed as a Perl framework to support many different types of POP and email servers, Mobile POP Relay is useful for mobile users. Once a user successfully authenticates against a POP server, relaying is allowed through the server for a specified time period. It supports Ipop3d, Qpopper, and Vpopd with Sendmail or Exim.
Net_NNTP is a PHP/PEAR library for communication with NNTP servers. Net_NNTP handles connection and protocol-level commands (RFC977), including many non-standard commands (RFC2980), via a user-friendly API which hides the actual NNTP commands/syntax. Some knowledge about NNTP and general knowledge about email and MIME is required, since parsing of content and headers is left up to the user. Net_NNTP allows advanced users direct usage of NNTP commands via the separate protocol implementation. Net_NNTP includes a fully-functional NNTP to HTML gateway demo application.
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".