How can I use PGP with my mail software?
PGP support is available for most of the popular e-mail software, with varying success. A quick search on a search engine should reveal the various tools/configurations/plugins specific to your mailer.
Although it's convenient to integrate PGP with the mailer software, it can be used separately to generate signed messages. Therefore, you can send signed messages, even if you can't find a suitable extension to your mailer software.