Navigate to the Segment you wish to enable Notifications for.
Next click on the Bell icon on the right hand side of the page and select the options that apply [see below].
Disable Notifications: choose this option to receive no notifications.
Send Notifications for my Accounts: Choose this option to receive notifications for accounts assigned to YOU.
Send Notifications for all Accounts: Choose this option to receive a Notification when any account is added to this Segment.
Make sure to check the Send to Email box to ensure you receive your notifications.