How to attach a digital certificate for mail to a letter in php?

Question

PHP

Good day everyone.
Tried to get Google to answer my question, but either the question is not popular on the Russian Internet, or I'm setting the search parameters incorrectly.
In general, the task is simple: there is a certificate for signing e-mail from Entrust. I need to attach it to messages that I send through the php mail() function.
Maybe? If yes, then who will tell you how?
Thank you all in advance.

Answer 1

If I'm not mistaken, it's www.php.net/manual/en/function.openssl-pkcs7-sign.php