At one point, I was able to get an S/MIME setup going in Mail.app, and it would automatically encrypt emails sent to others whom had previously sent me a signed

At one point, I was able to get an S/MIME setup going in Mail.app, and it would automatically encrypt emails sent to others whom had previously sent me a signed message. Unfortunately, there were tons of mailing lists and clients that would choke even on the signed messages, plus renewing the certificate and all that was too time consuming.