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

[Dave]

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