Giacomo I understand you have heavy Friday 
We need to resolve it from 3 point:
- I love your distro to much
- From company point of view it’s not possible control your domain outgoing emails when you put this task at your employees
- NS will not compile with lot of regulations like ISO, etc
And DKIM is not a crypto future this is just another way to validate original sender of message.
PGP is completely different from it.