Threat actors are increasingly using email bombing to bypass security protocols and facilitate further malicious endeavors.
Email bombing, known also as a “spam bomb,” involves flooding a target’s email inbox with a massive volume of emails, overwhelming the recipient and disguising potential phishing or credential theft attempts.
Understanding Email Bombing
Email bombing works by attackers signing up victims to numerous subscription services, resulting in a deluge of confirmation emails.
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This tactic often goes undetected by traditional email security gateways because these emails are not inherently classified as spam, as they come from legitimate sources.
This was observed in an incident in early 2025 where Darktrace’s security solutions identified an email bombing campaign targeting a customer.
In February 2025, Darktrace detected an email bombing attack where a user was inundated with over 150 emails from 107 unique domains in less than five minutes.
These emails bypassed a widely used Security Email Gateway (SEG) but were caught by Darktrace’s behavioral analysis tool, /EMAIL.
The emails varied from languages and topics, most commonly themed around account registration, indicating a mass signup to various services.
The emails were sent using reputable marketing platforms like Mailchimp’s Mandrill, enhancing their apparent legitimacy.
Despite the benign content of individual emails, the sheer volume created a disruptive swarm effect.
Darktrace’s AI-driven /EMAIL product identified this unusual activity and would have prevented emails from reaching the recipient’s inbox if set to Autonomous Response mode.
Post-Bombing Tactics and Consequences
Following the email bombing, attackers attempted to engage the victim via Microsoft Teams, impersonating the IT department to exploit a sense of urgency.
The victim, likely overwhelmed, engaged in the call and subsequently disclosed their credentials.
The attacker then leveraged Microsoft Quick Access, a legitimate tool, for malicious purposes, performing reconnaissance on the network to prepare for further exploitation.
The attack escalated as the compromised device began scanning the network, attempting to connect to internal systems, and making multiple failed login attempts.
Darktrace’s Cyber AI Analyst grouped these activities into a single incident, highlighting critical stages of the attack, including LDAP reconnaissance and significant connection attempts over port 445.
Had Darktrace’s autonomous response capabilities been fully enabled, it would have promptly intervened by blocking suspicious connections, significantly reducing the attack’s impact.
This case underscores the sophistication of modern cyber threats and the importance of advanced AI security solutions like Darktrace, which can detect and mitigate such attacks without the latency common in traditional security systems.
Email bombing, when combined with social engineering and insider threats, poses a considerable risk to organizational security, highlighting the need for proactive and adaptive security measures.
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