Transactional and lifecycle mail share a brand, so one bad campaign can degrade password-reset delivery.
What email account takeover is#
Account takeover (ATO) is unauthorized access to a legitimate mailbox, typically via phished credentials, password reuse, or OAuth consent phishing.
Why it matters#
A taken-over mailbox bypasses every authentication control and becomes a launchpad for BEC and internal phishing.
Implementation plan for SaaS companies#
- 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.
Priorities specific to SaaS companies#
Transactional and lifecycle mail share a brand, so one bad campaign can degrade password-reset delivery. Weight your effort toward the steps above that address this constraint first, and measure with metrics that match how SaaS companies generate value from email.
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.