I just wonder if there is a way to use SSL certificates or PGP keys for signing my email.
At the moment I have to setup S/MIME in Outlook (or another thick client) to send signed messages via SMTP. It works for me, but I'm looking for a way to do the same using GMail's web interface.
FireGPG can use GnuPG, but I couldn't find any mention of S/MIME.
Gmail S/MIME plugin for firefox.