A. Microsoft has released a tool that lets you send custom messages to users who exceed their mailbox quotas. You can download the tool from http://www.microsoft.com/downloads/details.aspx?familyid=EB52F6AB-E07A-476C-B32B-145AF6EA970C&displaylang=en. You can use the tool with Exchange Server 2003 and Exchange 2000 Server (Exchange 2000 requires a hotfix, which you can download at http://support.microsoft.com/?kbid=824312). You can find additional information about the service at http://msexchangeteam.com/archive/2004/04/20/117024.aspx.
The tool basically turns off the system-generated quota messages and substitutes its own component that lets you define a custom quota message.