I have put a link with more info about this if you don’t want to use Actalis

Updated, thanks!

I don’t think it’s possible to do that, but I have no experience on this since I don’t use my own email server so I could very well be wrong.

Awesome, i spent a long time writing it and I’m happy you find it useful!

So as I understand :

1. Actalis is a trusted authority among others but is the only one to issue free S/MIME certificates that I found. You need to use a trusted authority to make the signature, or else your email client will say “Cannot verify signature authenticity” and show a red badge. This explains it better
2. When you sign your email, you include your public key in the signature. So just sign every email (usually an option in your client) to let anyone you email have your public key. I don’t really understand why you would need to change stuff in the email server.