By any chance, are the "Over Quota" notices coming from your email provider?
If so, then you need to take care of the problem by
a) deleting excess emails from the server (login via webmail to do so), and
b) prevent this from happening again in the future. Go to Tools, Accounts, select
the account, Properties, Advanced. Near the bottom, there is an option for
of the two 'Remove' options.
Gary VanderMolen [MS-MVP WLM]