TLS Certificates (Mac OS X Mail)

Well, I don’t know if the Snow Leopard Mail app had support for these or not, but Mail on Lion certainly does, as when setting up an account in preferences there is now an option to designate a TLS certificate for encrypting/signing your e-mails.

What I’m interested in is what the best way to start doing this is? I think that these technologies are going to be more and more important in re-establishing trust to e-mail, so I’d like to start being able to at least sign my messages so people can know that it’s me sending them.

I’m wondering though where is the best place to get certificates for this purpose, are free certificates something that Dreamhost could support for e-mail accounts, acting as a certificate authority to verify the sender of an e-mail actually is the dreamhost user they are claiming to be?

Has anyone else here set up encryption and/or signing for e-mails via their Dreamhost account(s), if so, how did you go about it?