don’t let save setting

the phpmailer FUNCTION sign is here. it is in PHP 4 since 2007

PHPMailer::sign() – Set the public and private key files and password for S/MIME signing.
https://genesis.wp-a2z.org/oik_api/phpmailersign/

i’m just hasking how to find a plugin that use this function to sign all the wordpress out mail.