The DigestNotificationQueue is used by the notification service to queue requests to send mail. Requests are queued to send digest notification emails for notification subscriptions that are to be delivered according to a schedule rather than immediately. The subscription user interface allows users to select the delivery method when subscribing to an object. A preference can be set at the Site level or the Organization level to set the delivery time for digest notifications. The Organization level preference applies to users in that organization, the Site level preference applies to users not covered by an Organization level preference. Requests are queued on the DigestNotificationQueue for each unique preference value to schedule the delivery of digest notification emails, and these requests deliver the digest notification email to any user covered by the preference represented by the request.