Combat Email Bombs: Essential Strategies for Prevention and Response

This type of email attack is particularly difficult to defend against as automated bots are used to subscribe an email address to several lists per second. This article will discuss methods for surviving an email bomb attack, as well as ways to prevent an attack from occurring.

What Are Email Bomb Attacks?

An email bomb attack is commonly used to hide important notifications about account activity from victims in order to facilitate fraudulent online transactions. An email bomb uses a denial of service attack (DoS) against an email server to render accounts unusable or even cause network downtime. Spamming the inbox distracts from the real damage going on behind the scenes. Note that to understand the extent of an email bomb attack fully, it’s essential to familiarize yourself with the differentiation between spam vs scam emails and their respective attacks.

Attackers use email bomb attacks for more than disruption. Victims may see fraudulent charges on shopping accounts or watch their addresses become unusable for regular communication. These attacks aren’t always isolated. They can repeat this process, often by exploiting legitimate services, such as mass newsletter sign-ups. To stay ahead of these risks, organizations should focus on protecting their organization from cyber threats by leveraging effective Gmail security solutions, which provide stronger defenses against malicious email activity.

The tactic isn’t new. In the late 1990s, journalists critical of certain groups were frequent targets, and the method has continued to evolve ever since.

The tactic hasn’t gone away—it has simply broadened. Today, the targets can be almost anyone: government officials, policymakers, healthcare providers, emergency response teams, and more.

 In early 2025, Forbes reported on the Black Basta Attack, a cybercrime group using a modern email bomb attack to overwhelm Microsoft users with nonstop emails. Once inboxes were flooded, attackers followed up with impersonation attempts on Microsoft Teams. This mix of phishing and email bombs shows how today’s criminals combine email flooding attacks with social engineering to slip past traditional defenses.

Modern email bomb attacks are becoming more sophisticated. They can overwhelm most spam filters, flood employees' inboxes, and disrupt an organization’s communication.

How Do Email Bombs Work?

The methods of an email bomb attack vary, but most manipulate newsletter sign-ups from legitimate websites. Attackers use automated bots to find forms that don’t require authentication. Once the attack order is scheduled, the bots sign the victim up for thousands of newsletters at once.

The result is a nonstop flood of unwanted emails. The messages don’t stop until the victim unsubscribes from each service one by one—a process that can take hours or days. This tactic makes email bomb attacks difficult to stop without strong spam filter protection or other advanced defenses.

Quick fact: Beyond the flood of unwanted emails, email bomb attacks often open the door to scams and fraudulent transactions. Solutions that specifically target email threat scamming provide the advanced filtering needed to block these threats.

The Price of Email Bomb Attacks on the Dark Web

Once a victim is attacked, they are often added to additional spam lists, phishing attacks, and email bombs, and malicious email subscriptions maintained by attackers. These lists are frequently shared or sold as part of dark web email bomb services, where cybercriminals advertise vulnerable accounts and promote tools for launching a new email bomb attack.

Sellers usually ask only for the victim’s email address and the desired start time for the attack. Unfortunately, there are countless marketplaces offering these services, making distributed spam attacks and email DoS attacks easy to carry out

The price of email bombs may vary; however, a typical seller charges around $15 per 5,000 messages, and most sellers offer price breaks for higher quantities, such as $30 for 20,000 messages. The U.S. Health Sector Cybersecurity Coordination Center has issued an advisory on mail-bombing attacks, and dark-web research shows mailing and spam services trade at low prices—evidence that email flooding attacks are both accessible and actionable for attackers. This low-cost ecosystem emphasizes the importance of spam filter protection and multi-factor authentication for email security as part of any spam attack prevention strategy. 

Understanding the low cost and accessibility of these attacks is only half the picture—the next challenge is knowing how to respond in real time and what measures to take if your organization becomes the target of an email bomb attack.

What to Do During an Email Bomb Attack

The challenge isn’t just recognizing an email bomb attack—it’s knowing how to survive an email bomb attack in progress while also reducing the chance of repeat incidents. Because any valid address can be flooded at will, preparation is critical.

Prepare for an Email Bomb Attack

• Require confirmation before newsletter subscriptions go live. This prevents attackers from using bulk sign-ups to weaponize mailing lists.
• Keep all mail delivery software patched and current, and ensure antivirus protection is active.
• Block common file types tied to bomb attacks (.zip, .7z, .exe, .rar) before they hit inboxes.
• Set a maximum email attachment size to reduce the risk of large payload floods.
• Configure auto-responses—like out-of-office or bounce messages—to trigger only once, preventing mail loops that amplify the attack.
• Ensure out-of-office, bounce back, and other automatic messages are only sent once to prevent an endless loop of recurring automatic replies.
• Limit send permissions to only internal and authorized users, who may send to distribution lists.
• Implement security tools like multi-factor authentication for passwords, and never use the same password twice.
• Implement a cloud email security provider that's equipped to protect against attacks and has a significant relationship with its clients to understand typical mail flows as well as identify attacks.

Monitor Suspicious Account Activity

• Installing proper spam protection measures instead of simply deleting emails in mass is a proactive way of thinking ahead of an email bomb attack.
• Critical inboxes for your organization should use failover services and notifications to protect against important emails being deleted.
• Use a bulk mail filter to help stop subscription-based emails from landing in the inbox by adding the newsletters to your approved sender’s list.
• Use custom spam filters to help block emails that contain words like “confirmation,” “subscription,” or “confirm.”
• Make sure that online passwords are changed and that all of your organization’s online accounts are secured with multi-factor authentication.
• Look for suspicious activity, such as unauthorized withdrawals or purchase confirmation emails that may not have been noticed during the attack, and delete any emails.

 Common FAQs on Email Bombs:  

What is the difference between email bombing attacks and traditional spam?

Spam fills inboxes with ads or junk offers. Email bombing is different. Attackers send thousands of messages in minutes to bury important mail. Spam is annoying. An email bomb can block business and hide fraud.

How can I tell if my business is under an email bomb attack?

Watch for sudden spikes. If thousands of random emails hit your inbox or forms at once, that’s a sign. Messages often come from many senders with no clear pattern. If real emails slow down or disappear in the clutter, you’re likely under attack.

What email security measures prevent email bombing attacks?

Strong filters are key. Use security tools that catch traffic spikes fast. Add limits on form requests and use CAPTCHA to stop bots. Layered defenses and log monitoring make it harder for attacks to slip through.

How do I recover from an email bombing attack and prevent future incidents?

First, stop the surge. Work with your provider to block junk traffic. Then check for alerts or fraud that may have been hidden. Once stable, add better filters, stricter limits, and monitoring so it doesn’t happen again.

The Bottom Line: Protecting Against Spam Attacks and Email Bombs

Email bombing is an attack that devastates productivity and sometimes only becomes apparent once it's already too late to act. Variants of distributed spam attacks and email DoS attacks have been around for years, but automation has lowered the barrier to entry. Attack kits on the Dark Web cost less than you think, which means anyone with a grudge or a goal can aim thousands of messages at a target.

Email remains central to business, but the same reliance makes it a constant target. Strengthening defenses means going beyond the basics. A managed security layer can complement existing controls and give better coverage against modern email threats. Training matters just as much. When employees know how to recognize suspicious activity, they can often interrupt an attack before it causes harm.

If you’re rethinking defenses, start small but smart. Guardian Digital offers free email security best practices you can implement right away, and our multi-tiered security policy controls help build lasting resilience against email bomb attacks.