If these clients *know* you, and *trust* you, and know anything about security, there is no reason why you couldn't get away with a self-signed cert.If not, http://www.instantssl.com/
I can second this. I will be buying my mail server certs through InstantSSL in a few weeks. So far, I've heard nothing but good things about them, and their prices are excellent.
(No, I don't work there.) -- gentoo-user@gentoo.org mailing list
