Sendmail\Postfix + Milter\Mimedefang: how to encrypt and sign and emails?

I want to encrypt and sign all emails. In console this is possible by following lines:

openssl smime -sign -in ml.txt -signer my.pem -text \
    | openssl smime -encrypt 开发者_如何学运维-out mail.msg \
    -from steve@openssl.org -to someone@somewhere \
    -subject "Signed and Encrypted message" -des3 user.pem

I have installed postfix (or if it necessarily sendmail) and mimdefang. How to setup mimdefang or other daemon that use milter API to catch all emails sign and encrypt them and send to the recipients?