Microsoft have added gmail support to Cortana so you can have Cortana access our Google calendar, contacts and mail. From Cortana you click on your Cortana Notebook, select Connect Services and add a Service, select gmail and then sign in to your Google account. It works with Google Apps accounts as well as standard Google accounts. It should mean you can reminders, notification of package tracking and other helpful services from Cortana even when using Google’s mail system.