In Exchange 2007 Standard Edition a mailbox server can only hold 5 databases (public folder or mailbox).
In Exchange 2010 Standard Edition a mailbox server can only hold 5 databases (public folder or mailbox).
In Exchange 2007 Enterprise Edition a mailbox server can hold 50 databases (public folder or mailbox).
In Exchange 2010 Enterprise Edition a mailbox server can hold 100 databases (public folder or mailbox).
Alıntı : http://computersplace.net/microsoft-releated/windows-server-howto/exchange-20072010-maximum-databases.html