Actually ... (Score 1)

Exchange standard edition versions 4, 5, and 5.5 all have a database limit of 16GBs.

http://support.microsoft.com/default.aspx?scid=kb; EN-US;185457

Enterprise edition is needed to surpass this limit.

Also exchange database files are .edb files not .mdb

These same principles hold true for exchange 2000 and 2003.