Clear email system notification after email read

It might be a nice way to help the user keep their notification tray clean if we cleared the new email notification from the notification tray if they opened an email the notification references (user doesn't click on notification, but ignores it and goes to Mail later on their own).

1. I get a notification of a new email from Santa.
2. I know that's preposterous so I ignore the notification.
3. I open Mail and read why someone named Santa is trying to scam me.
4. The new mail notification still persists in my system notifications tray.

It would be nice if that new email notification cleared automatically by me opening the email.

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