Hato is developed with the latest version of Chicken, available from
http://www.call-with-current-continuation.org/
Hato has some prerequisites available from Chicken’s free library repository. If you don’t have them already, you can install them all with the following command:
# chicken-setup gdbm tcp-server autoload charconv sandbox openssl
You can then compile and install hato with the following:
# make # make install
You could also run directly from the source directory, skipping the "make install" step. Note this step currently just copies into /usr/local/bin/ - it doesn’t setup init scripts or otherwise interfere with any existing mail server.