[Dovecot] Purging a large folder... anything I need to be careful of?

I've got a large message folder (about 40G in 'cur') that I need to empty to a more reasonable size. Oddly, my Thunderbird e-mail client only sees about 2.4G of that, and has "looped" a few times. What I mean is, I thought someone was cleaning the folder out, but Thunderbird apparently was actually just looping back to 0 every 4 gigs and starting to count up again Ha. But that's a sidenote. So, since Thunderbird apparently is not seeing all of the messages, what is the safest way to delete the files straight from the 'cur' folder? IS that safe? Will I mess up any of the dovecot indexes in any way?? Dave