I haven't fussed around with offline readers much, but I'll bet it'd be pretty simple to add a step to the collection/.ZIP process, which would encrypt the whole package with some prearranged key.
that's vulnerable...it's the secret key problem. The ELEGANT way to do this with encription is to just make a normal ZIP file, but then build diffie-hellman into your file downloader (zmodem). This is also the least work solution. SO, since we're talking about offline mail readers... Whats the best one for the PC that works (or can easily be made to work) with rfc822 mail files? There's pcelm, which sucks...and there's mush, which is slooooow as hell because of all the overlays. I was writing my own, but I got side-tracked...somebody want to save me some programming?