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.
dkimproxy is an SMTP proxy that signs and/or verifies Domain Keys Identified Mail (DKIM). It is designed to work with Postfix. It comprises two separate proxies: an "outbound" proxy for signing outgoing email, and an "inbound" proxy for verifying signatures of incoming email. With Postfix, the proxies can operate as either Before-Queue or After-Queue content filters.
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.
mysqmail-qmail-logger is a very small daemon that logs SMTP traffic such as successful delivery and relaying to an SQL database. It splits the information by domain and by users in both the to and from fields, which makes it very easy to count all the SMTP traffic for a given domain name.
mysqmail is a replacement for the qmail standard checkpasswd that performs authentication with a MySQL table. After authentication, it sets up two environment variables that it uses to perform traffic accounting. For SMTP, it provides an alternative logger for the qmail-send program. Instead of logs, it writes the traffic to a MySQL table for the related domain.
Mailonator is a system that guarantees the delivery of email attachments quickly and securely and avoiding any restrictions that might be in effect for the email recipient. Mailonator software installs on a server, so the email service and client tools never need to change. It works by intercepting email messages, stripping the attachments, and storing them on a server. In addition, Mailonator sends you an email notification when recipients download your attachment, and provides system administrators with usage statistics.