I've downloaded csmail.exe from your website. When I launch csmail.exe it installs a completely different program.

The most likely cause of this is that you have a file called setup.exe (which will actually be some other program's install utility) in the directory to which you downloaded csmail.exe.

A feature of the Winzip self extracting executable technology is that the existing setup.exe will be launched instead of the correct program.

Try moving csmail.exe into it's own directory and running it from there.