Account Takeover (ATO)

What is Account Takeover (ATO)?

Account takeover (ATO) occurs when an attacker gains unauthorized access to a user’s online account, such as an email inbox, cloud service, or administrative portal.

Once inside, the attacker can read sensitive messages, send mail as the victim, change account settings, and use the account to pivot to other systems. In email contexts, ATO is especially damaging because a compromised mailbox can be used to send credible phishing, bypass multi-factor protections, and harvest credentials or financial data.

How Account Takeover Happens

Attackers use many techniques to take over accounts, often combining them in campaigns designed to evade detection. Common methods include credential stuffing, phishing, social engineering, password reuse exploitation, and abusing weak or exposed APIs.

A typical scenario looks like this: stolen credentials from one breach are reused on a corporate email login, or a targeted phishing message convinces an employee to enter credentials on a fake login page. With access, the attacker may set up forwarding rules, modify signatures, or send messages from the victim to trusted contacts, increasing the chance of successful fraud.

Impact on Email Security and Deliverability

ATO undermines both security and trust. Compromised accounts are frequently used for business email compromise, invoice fraud, and internal reconnaissance. Because the messages originate from a legitimate, authenticated mailbox, they often bypass content filters and may pass SPF or DKIM checks, making DMARC the last line of defense.

Consequences include reputational damage, financial loss, regulatory exposure, and degraded deliverability. A pattern of ATO-driven abuse can lead mailbox providers to throttle or block a domain, hurting legitimate communications. Detecting ATO early is essential to limit both immediate harm and long-term brand impact.

Account Takeover and DMARCeye

DMARCeye helps organizations detect and investigate account takeover by making authentication and sending patterns visible. Aggregate DMARC reports reveal anomalies such as unexpected sending sources, sudden spikes in volume, or new forwarding behaviors that often accompany ATO.

By combining DMARC, SPF, DKIM results and metadata like ASN and IP history, DMARCeye highlights suspicious activity for fast response. This reduces reliance on manual log review and speeds remediation steps such as disabling compromised accounts, blocking rogue senders, and resetting credentials.

Sign up for a free trial of DMARCeye today and secure your email domain.

To learn more about DMARC and DMARC-related terms, explore the DMARCeye Glossary.