This program is designed to deliver bulletin messages to thousands of users on a system. If you want to deliver mail to a large number of people to be read through POP or a local email program (such as mutt) then the traditional approach has been to setup an alias to map to all the users. The problem with this is that mail delivery is very slow and even delivering to 1000 users on a fast machine can take a significant amount of time and system resources. Also if the message is large then you use a lot of disk space.
This program solves that problem by creating a single file with the message data and creating links to it from the ~/Maildir/new directory of every user who is in the group (it delivers mail based on Unix groups). This is fast (can deliver a bulletin to 30000 users in minutes on a slow machine), saves disk space, works with all Maildir client software, and makes it very easy to undeliver or modify a bulletin.