Encryption like this doesnt work

[Tons of PCs]

Any encryption where the key needs to be sent in a similar method to the message is insecure. 

[Christopher R. Wren]

That's why I suggest, in another thread, that the keys be exchanged via a secure back-channel, such as email signed with verified pgp/gpg keys.  I agree that the automatic key exchange is dangerous, but it's a nice convenience as long as you ALWAYS verify the keys via a secure channel.