I wonder if thunderbird (plus addons?) could help fight phishing in the following way. Say I need to check the authenticity of emails I get from Bob. Is there a way to 1) Get Bob to create digital signature (PGP?) and send it to me ahead of time in secure channel; I store this signature locally (on thunderbird?) 2) Bob sends me an email, with this signature 3) Upon receiving this email, thunderbird automatically verifies the signature against the locally saved one and confirms that the signature is correct Note: I am looking for automatic verification of message/sender, NOT encryption. If this can be done, do Bob also needs to use thunderbird (plus addons?), or is there a standard protocol for this (e.g. can this be done via gmail webinterface, outlook, etc?) THANKS! p.s. For (1), Bob can e.g. posts his signature on his webpage as well. But my main question is about (3).