Using El Capitan Apple Mail, what is this new message I am receiving on messages RECEIVED from folk's. The Message return address contains the NEW line: Security: (checkmark logo) Signed. On top of the return address in the message is the Apple message that: Apple Mail is Unable to verify message signature.
This is new to me in El Capitan, what is it?
This is new to me in El Capitan, what is it?