Thank you!

Yeah, wow, now that I look at it, this patch (a) puts a non-human-readable button into your account settings, (b) doesn't actually download all your messages when you check it unless you do some magic by manually deleting your cache file, (c) can't be applied to individual accounts or folders -- it's either all or nothing, and (d) can cause serious harm to your machine because it downloads all the mail to the /opt directory.

I've checked, and this patch is actually in the "stable" branch of CSSU. I think maybe it should remain only in the "testing" branch, until it gets a little more loving -- in particular, some work to ensure that it doesn't fill up all the space in /opt, or for that matter, wherever it deposits the mail. (I'm not sure I'd be able to fit all the e-mail in my various folders onto my SD card, let alone the /opt directory...)