A taken-over mailbox bypasses every authentication control and becomes a launchpad for BEC and internal phishing.
How to implement email account takeover#
- Enforce phishing-resistant MFA (FIDO2 keys or passkeys) for admins and finance.
- Review third-party OAuth grants monthly and restrict user consent.
- Alert on impossible-travel logins and mass downloads.
- Have a documented response: revoke sessions, reset, audit rules and forwards, notify affected parties.
How to verify it worked#
Send a test message to seed mailboxes at Gmail, Outlook, and Yahoo, then inspect the Authentication-Results and delivery headers. Repeat after any DNS or sending-platform change.
Common mistakes#
- SMS-based MFA for high-value accounts.
- Not checking forwarding rules after remediation.
Frequently asked questions#
What are signs of a compromised email account?
Unknown sent items, new forwarding rules, missing mail, login alerts from unfamiliar locations, and contacts reporting odd messages.