popbsmtpd watches syslog for successful POP and IMAP logins, and writes IP address entries to a database to permit SMTP mail relaying for a configurable duration. No changes to any other software are required, and it can process logins where the IP address and the authentication success are recorded on separate log entries (i.e., when using stunnel). It has a user-configurable scheme for recognizing and extracting values from log entries, making it possible to use with many POP and IMAP daemons without requiring any programming changes. These configurations can be tested using sample log data.
POPauthd is a Perl-based daemon that uses POP to authorize connecting hosts for SMTP relaying. It is particularly useful to authenticate roaming users with IP addresses that change often. The daemon runs in the background, watching the syslog for successful POP logins. When it sees one it enters the IP in sendmail's access database, giving the host authorization to relay through the server. The entries can be expired after a prescribed, configurable period of time with a companion script run via crontab.
PigeonDeliver is the delivery agent of the PigeonAir project, a solution to easily build up clustered, scalable, and modular email services. PigeonDeliver is modular in nature, allowing it to be used on Postfix and other MTAs using their own native APIs without performance loss. It allows mail services to be easily and transparently distributed among a cluster of mail server, easily supporting new services and new modules added using the PigeonDeliver API, which simplifies writing filters and/or delivery agents.
Postmaster is an Internet mail transport agent (MTA) that handles incoming ESMTP network connections and delivers accepted messages to the user's mailbox by piping it into an arbitrary local mailer (such as Procmail). It is configurable beyond anything you'll ever need, handles any number of concurrent connections without forking or using OS threading, and it is pretty efficient. It currently lacks any form of queue management, but for leaf sites that don't need to do extensive mail relaying, it is a reliable and powerful solution.