How Email encryption for the broader public could be realized

After reading the Every Email In UK To Be Monitored article and its comments over at Slashdot I once again felt like encrypting each and every Email I send using GPG/PGP. Now for this encryption to work the person I am sending a message to would need to have GPG/PGP set up too. A lot of technical-minded people already have this set up, but I can not expect everyone to be using encryption.

The reason for not everyone using GPG/PGP for encrypting their emails might be that, even though GPG/PGP have become a lot more usable for the end-user in the last few years, these programs are probably still too technical and thus hard to understand for non-technical users.

This is when I thought a little about how people could be made using public key encryption for E-Mails. After a bit of brain-storming an idea came to my mind, an idea I would like to present you with.

Basic idea

What about creating a program acting as both SMTP and POP3/IMAP proxy server that included all the logic to do encryption and would encrypt/decrypt messages transparently?
If this logic was moved out of Email clients we could get a solution working universally for each and every Email client out there.