S/MIME download public key

Question

If I want to send an S/MIME encrypted email using openssl_pkcs7_encrypt from my webserver to a list of customers. Where do I get the public key of the recievers from?

I read about a Certificate Revocation List but not sure how to access it. Also it looks like it's only contains invalid keys.

If found this search form but no idea...

Answer 1

You'd need your customers to provide their public keys. There's no canonical way of obtaining these.

Answer 2

Why don't you purchase a cert from a trusted CA and encrypt email with your private key while the public key will be included in the cert sent along with the email. Take a look at this class, I applied for 30 days trial of one trusted CA and tested it with that cert. http://lamp-dev.com/smime-email-encryptionsigning-using-zend_mail/100