I'm currently using Gmail through Thunderbird with IMAP so that I can digitally sign and encrypt my emails as well as work with emails that are digitally signed and encrypted. I like how, with IMAP, labeling can be done through the email client. I want to make some emails available locally (I honestly haven't decided on a policy yet, but I would like to be able to select certain emails, either individually or by tags) while having others only reside on the server (and if that means I have to go into Gmail to get them, I'm fine with that).
Can this be done? If so, how?