Bandwidth Montioring - Mail problem - Postfix

Hello all,

I'm having a problem with bandwidth monitoring -- it seems VERY inaccurate, specifically in mail (SMTP). I did just enable checking the rotated logs (checked "Include old rotated log files?"), so that may fix the problem. Any ideas what it might be if that doesn't fix it? I did compile postfix myself, so if there's some option (or some post-install option) I need to set, please let me know :)

Software versions: postfix 2.3.8 virtualmin 3.38.gpl webmin 1.330

Thanks, Phillip