There's a lot on the web about spoofing the email sender's address so if I was so inclined I could send an email to you and fake the return address to make it look like you (or anyone) sent it.

You bring you a second question. That is, would you change to a proprietary or new email system that didn't allow such? It's unlikely to happen soon as the old email standard, broken as it is, is so widely used.
Bob