Email is just data held in a computer somewhere, and any data can be read with the right expertise. Even downloading an email does not entirely remove any threat as there will be remnants and/or copies somewhere.
Conspiracy theorists will suggest that security organisations, (FBI, CIA, MI5 or 6, etc), also scan all emails searching for keywords in their war against terrorists and such. That may be true, but it doesn't really concern me.
So, yes, emails are insecure. But there are billions of emails being transported around the internet every day, so unless your friend is engaged in some nefarious activity, I am not sure how worried he should be.
Fax is just data transported down telephone lines to a receiver. Data? Possibly that can be intercepted as well. I'm not sure.
My 71 year old friend who knows nothing about computers, technology, etc but still works in investing wants an all in one printer with fax because he heard that if someone emails you a document it sits on the server till you get it and anyone can look at it. So he wants to fax to be more secure. Anyone hear of this theory or what he's talking about?