MacSOUP is an offline reader for Usenet newsgroups and Internet e-mail. If you don't know what newsgroups are, you probably don't need this program. MacSOUP is primarily a newsreader, its e-mail capabilities are somewhat rudimentary compared to "real" e-mail clients.
MacSOUP is free. I don't provide support for it; if it works for you, great - if it doesn't, too bad. I no longer actively work on it. I do try to keep it running on new versions of Mac OS (or macOS) as long as this is possible with reasonable effort, but if this becomes too much work, I'll stop doing it. This will definitely be the case if Apple removes the Carbon libraries from macOS, or stops supporting 32-bit applications.
I primarily keep MacSOUP available here for existing users; I don't recommend it for new users.
The current version of MacSOUP (2.8.5) is compatible with Mac OS X 10.5 through 10.11.