From: lmccarth@cs.umass.edu

Mike Ingle writes:

...

Instead of messing with user interfaces, you set the POP and SMTP addresses of your mail program to "localhost". You run locally a Visual Basic program that sits on ports 110 (POP) and 25 (SMTP) listening for connections. The VB program is configured with the addresses of your real SMTP and POP servers, and acts as a proxy.

...

When your mail program retrieves POP mail, it goes through the VB program, and the VB program decrypts any PGP mail it sees. When it sends mail, the VB program encrypts any mail it has a PGP key for the recipient of.

Would you be stuck if you wanted to send something unsigned and/or unencrypted ?

You'd put something into the mail message itself that would tell it "don't encrypt this" and/or "don't sign this". Hmm... you'd need to put in messages to be signed and/or encrypted your passphrase, or have it gotten some other way... which doesn't look very safe. Of course, if you're just encrypting it to the person's public key off of your keyring, and for stuff that's coming in encrypted to someone else's private key or signed with someone else's private key on your keyring, that wouldn't be so much of a problem. For the stuff coming in with the verification message (could be spoofed), looking for such strings already in an incoming message would be good. An attacker could still potentially slip something in between the mail program and the proxy program, though - the same problem as with the passphrase in the message. -Allen