Until October 2019 notification emails sent to region admins were automatic if you had add or edit permission in a region, you as an admin didn't have much control. There is only a profile setting to disable these admin emails site-wide.
We've now switched the admin notification system to use the "subscription" system that already exists, where a user can subscribe for updates on a region or particular trail. When you're assigned to a region as an admin with some permissions, your account is automatically also subscribed to that region with the corresponding features. For example, if you have edit permission, you are subscribed to edits in that region. You are also subscribed to a special new "admin" subscription option. This is the option that will send email notifications for items requiring admin approval. Such as pending new content, pending edits, abuse reports, or trail reports requiring approval.
Since admin notifications are now using the subscription system, you have the control to remove and edit your subscriptions to regions. You can also make your subscriptions more granular. If you are admin for a large region like a state, you can remove your subscription from the entire state, and instead manually subscribe to some of the sub regions you care about.
When someone adds you to a regions permissions, they have the option to un-select "subscribe to emails", doing this will NOT subscribe the user to the region.
Adding a user to a group that already has permissions in a region, will automatically subscribe that user to the regions the group has permissions.