Aside from GnuPG the other pre-requisites are:
A mail server for your domain with the full authority on the user mail addresses for this domain.
A Unix system where you have an account to receive mails to a dedicated mail address and to send mails via the sendmail tool. An account on the mail server will be the best choice.
A web server for the same domain to deliver static pages over TLS. Re-direction to a different server is possible
The ability to install the latest GnuPG version from source.