Galaxy brain idea: Just encrypt your messages manually. Agree on an algorithm and trade keys in-person, then send each other encrypted files that you decrypt with a separate program (and for added privacy, on a separate device that doesn't have network access). It's not convenient at all but the idea is hilarious.

There's an urban myth at my university that two students did this to test rumors that the school emails were being monitored, and after a few weeks later IT emailed them asking them to stop.