Should hourly email notification accumulate all the notification from past hours?

I am designing an email notification setting for an ERP.

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Based on the image above:

  1. User selected the 'Hourly' option for email notification.
  2. In the first hour away from the system, the user gets 3 new notifications and this update is emailed to the user "3 new notifications since your last login {date}{time}".
  3. For the 2nd-hour user is away, user gets 1 additional new notification.

Should the system send the second email as '4 new notifications'(total #notifications of all hours away) or '1 new notification'? (only #notification in that hour).

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