What Are Backscatter Emails?

Backscatter emails are auto-generated email bounce messages received by an individual for emails that they never sent. These messages are often perceived by recipients as unsolicited spam.



What Causes Backscatter Emails?

There are several causes of email backscatter, these include:

  1. Spoofing

    Perhaps the most common cause of backscatter emails is spoofing. This means that a spammer forged the “From” field in an email header, to make it appear as though the email has a legitimate sender.

  2. Misconfigured Email Servers

    Some email servers are configured to send Non-Delivery Reports (NDRs) or bounce messages without proper checks. This can cause legitimate but misdirected bounce-backs to reach unintended recipients.

  3. Malware

    Malicious software can infect computers and use them to send spoofed emails with the infected user’s address. Bounce-backs from these spoofed emails contribute to backscatter.



What Are the Negative Impacts of Backscatter?

Email backscatter can have negative effects on the recipient.


Inbox Overload:


Email management is difficult enough as it is. Receiving a bucket load of unwanted emails results in an overly cluttered inbox, making it even more difficult to keep track of important conversations.


Reputation Damage:


If spammers repeatedly use an email for spoofing attacks, then that address may be blacklisted by some servers.


Resource Drain:


Processing and filtering backscatter consumes bandwidth and computational resources, potentially impacting server performance and increasing operational costs.


False Security Alerts:


The recipient might perceive backscatter emails as a security issue. This leads to them worrying about securing their email account which won’t resolve the issue.



How to Prevent Backscatter

So how can users prevent email backscatter? Here are several ways to mitigate and prevent the issue.

  1. Implement SPF, DKIM, and DMARC Protocols:

    • SPF (Sender Policy Framework): This security protocol allows domain owners to specify which mail servers are permitted to send emails on behalf of their domain.


    • DKIM (DomainKeys Identified Mail): This adds a digital signature to emails, enabling recipients to verify that an email came from the specified domain and that it has not been altered.



  2. Configure Servers to Reject Emails During SMTP Transaction:

    Instead of accepting and then bouncing undeliverable emails, servers should reject invalid emails during the SMTP session. This way, the sending server, not the receiving server, handles the bounce.

  3. Maintain Accurate and Updated Email Lists:

    Regularly cleaning and updating email lists to remove invalid addresses reduces the chance of sending emails to non-existent addresses.



How to Filter Backscatter:

  1. Use Anti-Spam Software:

    Employ advanced anti-spam solutions that can recognize backscatter patterns and filter them out. These solutions often include heuristics and algorithms designed to detect common traits of backscatter.

  2. Set Up Server-Level Filtering:

    Configure mail servers to use filtering rules that identify and block backscatter. This might include checking for typical backscatter characteristics, such as specific wording in bounce messages and headers that indicate the message is a delivery failure notification.

  3. Blacklist Known Backscatter Sources:

    Maintain a blacklist of domains and IP addresses known to generate backscatter. While this requires regular updates and monitoring, it can be effective in reducing backscatter volumes.

  4. Email Filtering Services:

    Utilize third-party email filtering services that specialize in identifying and blocking backscatter and other types of spam.


By understanding what email backscatter is, recognizing its causes, and implementing prevention and filtering strategies, email users and administrators can mitigate the negative impacts and improve the overall email experience.

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