This means you will need a lot of disk space if you want to work with multiple groups of any size, or with binary groups. Regarding mail, it won't do HTML or MIME, at least I don't think so. Some of this may be Gravity's limitations but some is Hamster. So, if you rely on mail with a lot of rich text and HTML you will be disappointed. These instructions are only to get you started.
Hamster has lots of configuration doo-dad thingeys.
We will set up a newsgroup for threaded email. It is the same for local NNTP or SMTP or POP servers. Lets get started. If you did not download the zip file, get it now. There is no set up program.