Emails you when an unfamiliar manager account links to one of your clients, versus your allowed-managers list. A manager account (Google calls it an MCC) is an account that controls others - an unexpected link is a common account-takeover route, because it grants broad control in one step.
Defaults & settings
Alert on any new manager link - when off (default), only truly unfamiliar managers versus your baseline alert; when on, every new link alerts, even ones you might expect.
Manage allowed managers - edit the list of trusted manager accounts.
Checks every 5 minutes; 7-day cooldown.
Example. A "growth agency" cold-emails your client, talks them into "a quick audit", and sends a manager link request the client accepts. The moment the link lands, you're emailed - and can have the conversation before anyone else has their hands on the account.