Knowing when your cap is almost at its maximum is important for ensuring that your lead flow is not interrupted. This notification is useful in letting you know to contact your support rep to raise your account cap.
To set this up, go to Settings, then Notifications.
Click on New > System Notifications > Account Lead Quantity Subscription Notification.
From here, select whether you want to receive an email or SMS (This requires a valid mobile number on the user).
Set your Quantity Limit to within how many you want to be notified for and click OK.