This guide is geared towards Web of Trust. I think most Email clients implement PKI functionality in one way or another. I've tried to set up Outlook with gpg4w

This guide is geared towards Web of Trust. I think most Email clients implement PKI functionality in one way or another. I've tried to set up Outlook with gpg4win (in a business environment) to work with WoT and it wasn't fun, although definitely not impossible. The easy way to solve any problems I had was to switch everybody to Thunderbird. But again, that's because I wanted to use WoT. If you want PKI, no need to install anything.