How to change size limitation warning te

I would like to change the text of the warning message sent to users who’s mailbox is reaching it’s size limit. We are finding the default message to be a bit harsh and it is causing an increase in helpdesk calls about mail not being sent or received. I have found reference to misspellings in the message, the white papers mention Mdbsz.dll as the culprit. Where do I change the text for this message.