The Full Contact List
The full list is under Organization Settings:
Unchecking the box in the first column will "Globally Deactivate" the contact. This sets them inactive on all Teams and removes them from the list of contacts offered in To and CC fields. Any email address which is no longer valid should be deactivated.
On a project's Team list there is a vertical ellipsis that reveals a menu where a contact can also be set globally inactive (or removed from this one Team).
The first column shows a multiselect button so you can select many contact then click the "Remove from Team" button that will be revealed.
Tonic detects bounced emails. If a notification previously sent to an email address has bounced, you'll see a marker next to that contact. You can still send to this contact, and if an email doesn't bounce, the hint will cleared automatically.
There are other hints too, like a house for "home addresses" like gmail and yahoo.