Go to your email settings and click on the Send and Receive settings. Check to see what your update schedule is set at. There is a separate setting for peak time and off peak time. The default setting for peak time M-F 8 am to 8 pm. The default is check for new mail every 15 minutes during peak time and not to check (set to manual) during off peak times. You can set it to check as often as every 5 minutes.