Confirm the inbox is actively compromised
Business Email Compromise (BEC) attackers usually sit quietly in the inbox for days before launching invoice scams. Confirming what's been sent and what rules they've planted is step one.
Where attackers hide
- Forwarding rules that send copies to an external address
- Filters that auto-delete replies from finance teams
- OAuth-connected apps that re-establish access if you change the password
- Hidden delegated-mailbox permissions