This is kinda built in already if you use the ubb control panel to send news letters.
In the registration section of ubb their is a field called:
Receive Administrator Emails:
The default is "hide" so the user never sees it on registration. But is set to true as default
If you change the setting to show and or require, the user can opt for or against notification.
Then when you send a mass email the user will get the notice.
Other than that you could set a custom registration field and run a query against that to determine who gets the notice. Some pushups would be required for this option though.