j-XChange is a pure Java implementation of the entire Collaboration Data Objects (CDO 1.21) library for accessing Microsoft Exchange Server in a platform independent manner. This library will allow interoperability with MS Exchange from all non-Windows platforms that support Java. This library is powered by j-Interop.
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.
purepost is an interface between Courier-MTA and Sophie for virus scanning. You can have it check mail for all your users, or just a few. Using courier's dot-courier functionality, this script intercepts an email before it hits the mailbox, creates a temporary file, tells sophie to scan that temporary file for viruses, and if it finds a virus, denies delivery and notifies the sender (otherwise it allows the message to be delivered).