If you do not already have AI turned on, toggle this feature to On. Then do the same for Send Alerts.
In the Alert Recipients option, click the Edit button to add yourself and/or other users in the database to receive the alerts. In the window that appears, type in your name or the name of another user, then click the green Edit Alert Recipients button.
With this feature turned on, AI will watch for any transactions over the limit and send an email for those that are. If you add or edit old transactions, AI will check those, too. Furthermore, AI will not automatically import transactions in the Pending Imports page that are over the limit but instead will alert you.