Limiting Mailbox Size

you do this from Exchange Admin client either on the server or a workstation that has it installed.

you have to be an excahnge admin.

then, either at the user properties under limits, "information store storage limits" you put in the limits. Or, at the Private Information Store properties under SiteName, servers, server name, private information store you put in limits that apply to all users.

limits are in size of K. So, 10Meg would be 10,000.

Do a search on this site. In the search box put Exchange Server. Scroll down to the section that specifies downloads and you should see this:

Manage Exchange distribution lists and mailboxes with help from our download

This will give alot of good advice on settings to tweak your Exchange Server. It should be the first link.