I had an 8GB .edb file and a 25GB .stm file on my Exchange 2000 Server machine. Why didn't the file sizes change when I moved 2GB of mailboxes?

Exchange keeps a database's .edb and .stm files open as long as that database is mounted, so you won't see the database's size change from within Windows Explorer or the command line. Therefore, the databases might be larger or smaller than the size you see in those places. Moving mailboxes out of a database doesn't make it get any smaller; it just increases the amount of unallocated white space in the database file. Each day, the Information Store (IS) performs an online defragmentation, which rearranges database pages to make the white space contiguous. If you want to shrink the database by removing white space, you must dismount the database and perform an offline defragmentation. The Microsoft articles "XADM: How to Defragment with the Eseutil Utility (Eseutil.exe)" at http://support.microsoft.com/support/kb/articles/q192/1/85.asp and "XADM: Online Defragmentation Does Not Reduce Size of .edb Files" at http://support.micro soft.com/support/kb/articles/q256/3/52.asp provide more information about defragmentation. In most cases, however, removing the white space isn't necessary—Exchange will use the white space in the database when it needs room for expansion. Because you might not be able to start the Store after you stop it, I recommend against doing offline defrags except when you're in desperate, bet-your-job need of space.