Using Mozilla Thunderbird as email client rather than Outlook

Is there some way that I can use Mozilla Thunderbird to send and receive Open PGP encrypted emails rather than having to use Outlook? If not, can Gmail be used directly or is Open PGP designed to work exclusively with Outlook in a Windows environment?

Yes, you can use Thunderbird with OpenPGP.
In Thunderbird you have to install an extension: Enigmail, the latest version is 1.5.1.
Enigmail adds OpenPGP messsage encryption amd authentication to Thunderbird. It features automatic encryption, decryption and integrated key management functionality.
In the menu you get an additional dropdown menu: OpenPGP, and in the toolbars you get extra buttons.
It works fine.

Sure !
Install the “enigmail” extension. It works super fine.

(by the way, I never succeded in getting the outlook extension to work properly…)

Many thanks Ole Junker and JP Cqvb! I really don’t like Outlook.