Issue with Exchange 2003 store size limit

Hi, Successfully installed a new server with windows 2000 server sp4 and exchange 2003 sp2. Private information store reaching 16gb limit after cleaning out white space etc,. I used the registry hack to succesfully increase the store size to 40gb and after restarting stores all seemed ok.

The problem? the physical store size has jumped a from under 20gb to 33gb in a few days, did some maintenance (reduced deleted retention times) and online defrag indicates about 6gb white space. However still seems way to high, I have estimated mailbox sizes through System Manager and guess size should be 18gb. Stm is only about 2gb.

Am I missing something – anyone come across this before. Thanks in advance.