Summary
If you are receiving bounce messages for emails you never sent, your domain is likely a victim of 'backscatter spam,' also known as 'bounce spam' or 'backscatter DSNs.' This issue arises when spammers forge your domain as the sender in their unsolicited email campaigns. When these illegitimate emails are sent to non-existent or blocked recipients, the receiving mail servers reject them and generate non-delivery reports (NDRs) or bounce messages. Because your domain was listed as the forged sender, these unwanted bounce notifications are then directed back to your inbox, making it appear as though you sent the original, undeliverable emails. This flood of unrequested bounces can impact your domain's reputation and signifies that your domain is being actively spoofed.
Key findings
- Definition of Backscatter: Unwanted bounce messages for emails you didn't send are primarily a symptom of 'backscatter spam,' also known as 'bounce spam' or 'backscatter DSNs.' This phenomenon occurs when spammers exploit Non-Delivery Reports (NDRs).
- Email Spoofing as Cause: The root cause of backscatter is email spoofing, where malicious actors forge your domain's email address in the 'From' line or 'MAIL FROM' address for their unsolicited bulk email campaigns.
- Misdirected Bounce Messages: When these spoofed emails are sent to invalid or non-existent recipients, or are rejected by receiving mail servers for other reasons, the resulting bounce messages are mistakenly sent back to your legitimate domain, as it was the address listed in the forged sender field.
- Indicators and Impact: Observing an excessive number of bounce messages, potentially exceeding the volume of emails you actually send, is a strong indicator that your domain is being used for spoofing. This unwanted traffic can fill your inbox with NDRs and indicates your domain's reputation is at risk, potentially leading to blacklisting.
Key considerations
- Implement Authentication Protocols: Implementing and properly configuring email authentication protocols, specifically SPF, DKIM, and DMARC, is crucial to prevent your domain from being easily spoofed. These measures allow recipient servers to verify the legitimacy of emails originating from your domain.
- Early Rejection of Spoofed Emails: Robust authentication helps recipient servers reject spoofed messages early in the process, before they can generate backscatter. This reduces the volume of unwanted bounce messages.
- Protect Your Reputation: Proactively addressing backscatter spam through authentication strengthens your domain's security posture and helps protect your sender reputation from being harmed by malicious actors.
What email marketers say
11 marketer opinions
Receiving bounce messages for emails you never dispatched from your domain is a clear indicator that your email address is being spoofed by malicious third parties. This common cybersecurity concern, often termed 'backscatter spam,' occurs when spammers fraudulently use your domain as the sender's address in their unsolicited email campaigns. When these illegitimate messages reach invalid or non-existent mailboxes, the recipient servers reject them and automatically generate non-delivery reports. Crucially, because your domain was the forged source, these bounce notifications are routed back to your own inbox, creating unwanted traffic and suggesting your domain is originating problematic email.
Key opinions
- Backscatter as a Symptom: The influx of bounce messages for unsolicited emails is a symptom of 'backscatter spam,' a consequence of your domain being exploited by spammers.
- Forged Sender's Address: Spammers leverage email spoofing to forge your domain's email address as the 'From' or sender's address, making their illegitimate messages appear to originate from your legitimate domain.
- Bounce Message Misdirection: When these spoofed emails target invalid or non-existent recipients, or are otherwise rejected, the resulting non-delivery reports are automatically sent to the forged sender, which is your domain, filling your inbox with unwanted notifications.
- Domain Reputation at Risk: Beyond the nuisance of unwanted bounces, this activity signals that your domain is being used for malicious purposes, potentially harming your sender reputation and increasing the risk of your legitimate emails being flagged or blacklisted.
Key considerations
- Essential Email Authentication: Implementing and correctly configuring email authentication protocols, particularly SPF, DKIM, and DMARC, is critical to validate the authenticity of emails sent from your domain and to prevent unauthorized use.
- DMARC's Role in Policy Enforcement: DMARC allows you to instruct recipient mail servers on how to handle emails that fail authentication, such as quarantining or rejecting spoofed messages before they can generate backscatter and return to your domain.
- Reputation Management: Proactive deployment of these authentication standards not only reduces unwanted bounce traffic but also significantly fortifies your domain's sender reputation, ensuring your legitimate emails reach their intended recipients.
Marketer view
Marketer from Email Geeks explains observing a very high volume of bounces, over 200% of emails sent, for @wanadoo.fr addresses with a '550 5.1.1 Invalid recipient' error. After investigating, they discovered that these bounced addresses were unknown and emails had not been sent to them, suggesting a potential external issue or bug with the recipient's mail servers.
25 Oct 2022 - Email Geeks
Marketer view
Email marketer from Twilio SendGrid explains that receiving bounce messages for emails you didn't send is a common problem known as 'backscatter spam.' This happens when spammers use your domain as the forged 'From' address for their spam campaigns. When these illegitimate emails fail to deliver, the bounce message is returned to your domain, making it appear as though you sent the original email that bounced. Implementing strong authentication like SPF, DKIM, and DMARC is crucial to prevent your domain from being easily spoofed and used in such attacks.
12 Jul 2021 - Twilio SendGrid
What the experts say
3 expert opinions
Unexpectedly receiving a high volume of bounce messages for emails you never initiated from your domain is a strong indication of 'backscatter.' This occurs when spammers forge your domain as the sender in their unsolicited email campaigns. When these illegitimate messages are sent to invalid or non-existent recipients, the receiving servers reject them and generate non-delivery reports (NDRs). Because your domain was falsely listed as the sender, these unwanted bounce notifications are then mistakenly directed back to your inbox, creating the illusion that your domain originated problematic emails. This tactic, sometimes referred to as a 'Reverse-DNS DDoS amplification attack,' effectively weaponizes bounce messages against your domain, impacting your inbox and potentially your sender reputation.
Key opinions
- Understanding Backscatter: The phenomenon of receiving bounce messages for emails you didn't send is known as 'backscatter,' a common form of email abuse where your domain is unwillingly used by spammers.
- Domain Forgery by Spammers: Spammers are forging your email address or domain in the 'From' or 'MAIL FROM' line of their unsolicited messages. This makes it appear as though the spam originates from your legitimate domain.
- Misdirected Bounce Notifications: When these forged spam emails are sent to non-existent, invalid, or blocked email addresses, the receiving mail servers generate non-delivery reports (NDRs). These bounce messages are then mistakenly directed back to your domain, as it was the address listed as the sender.
- Indication of Domain Exploitation: An excessive volume of unexpected bounce messages, particularly those that surpass the number of emails you actually send, is a strong signal that your domain is being actively exploited and spoofed by malicious actors.
Key considerations
- Leverage Email Authentication: To effectively combat backscatter, it's essential to implement robust email authentication protocols such as SPF, DKIM, and especially DMARC. These standards help receiving mail servers verify that emails purporting to be from your domain are legitimate.
- Prevent Spoofing with DMARC Policies: A strong DMARC policy, set to quarantine or reject, can instruct recipient mail servers to block messages that fail authentication and appear to come from your domain. This prevents spoofed emails from even reaching their destination and generating bounce messages back to you.
- Safeguard Sender Reputation: Proactive steps to prevent domain spoofing not only reduce the influx of unwanted bounce messages but also critically protect your sender reputation, ensuring your legitimate email campaigns maintain high deliverability.
Expert view
Expert from Email Geeks explains that an excessive number of bounce messages for email addresses the sender didn't even send to, especially when the bounces exceed the number of emails sent, indicates that someone is forging the sender's domain in the 'from' line of their spam messages. These spammers create a fictitious email address using the legitimate sender's domain, send out spam, and when the receiving server rejects the mail, the bounce notifications are directed back to the legitimate domain owner instead of the actual spammer.
29 Jan 2024 - Email Geeks
Expert view
Expert from Spam Resource explains that receiving bounce messages for emails you didn't send from your domain is often due to "backscatter." This occurs when spammers forge your email address as the sender (the 'MAIL FROM' address) and send spam. If these spam messages go to invalid or non-existent recipients, the bounce messages are then sent back to your forged address, creating the illusion that you sent the original spam. This is a form of "Reverse-DNS DDoS amplification attack."
30 Jun 2023 - Spam Resource
What the documentation says
4 technical articles
A common reason for receiving bounce messages for emails you did not originate from your domain is a phenomenon known as 'backscatter' or 'bounce spam.' This situation arises when spammers or malicious actors exploit your domain by forging it as the sender address for their unsolicited bulk email campaigns. When these illegitimate emails are sent to non-existent, invalid, or otherwise undeliverable recipient mailboxes, the receiving mail servers generate Non-Delivery Reports, or NDRs. Because your domain was the fraudulently stated sender, these unwanted bounce messages are then automatically sent back to your legitimate domain, creating the impression that you sent the original undeliverable email.
Key findings
- Backscatter Explained: The phenomenon of receiving unexpected bounce messages for emails you did not send is widely referred to as 'backscatter,' or sometimes 'bounce spam' or 'backscatter DSNs,' indicating your domain is being used without authorization.
- Domain Forgery: This issue primarily stems from spammers forging your domain's email address as the sender in their bulk unsolicited emails. They manipulate the 'From' address to make their spam appear to originate from a legitimate source, which is your domain.
- Misdirected Non-Delivery Reports: When these spoofed emails are rejected by recipient servers-either due to invalid addresses or spam filters-the resulting Non-Delivery Reports (NDRs) or bounce messages are automatically routed back to your domain, which was listed as the forged sender.
- Reputation Impact: A significant influx of these unsolicited bounce messages can not only flood your inbox but also indicate potential harm to your domain's sender reputation, as it suggests your domain is associated with spam activity.
Key considerations
- Essential Authentication Protocols: To effectively combat backscatter and prevent domain spoofing, it is crucial to implement and correctly configure email authentication protocols such as SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance).
- Early Spam Rejection: These authentication methods enable recipient email servers to verify the legitimacy of incoming emails. By doing so, they can identify and reject spoofed messages early in the delivery process, preventing them from generating bounce messages that would otherwise return to your domain.
- Bolstering Deliverability: Properly deploying and maintaining these security measures not only reduces the volume of unwanted bounce messages you receive but also significantly improves your overall email deliverability by ensuring your legitimate emails are trusted and reach their intended recipients.
Technical article
Documentation from Microsoft Learn explains that receiving bounce messages for emails you didn't send from your domain is often due to 'backscatter DSNs' or 'bounce spam.' This occurs when spammers forge your domain as the sender in their unsolicited emails. When the recipient server rejects the spam, the non-delivery report (NDR) or bounce message is sent back to your domain, appearing as if your domain sent the original email. Implementing SPF, DKIM, and DMARC helps mitigate this by allowing recipient servers to verify legitimate senders and reject spoofed emails early.
31 May 2025 - Microsoft Learn
Technical article
Documentation from Google Workspace Admin Help states that if you're getting bounce messages for emails you didn't send, it's highly likely your domain is being spoofed by spammers. They explain that spammers often forge the 'From' address to make their unsolicited emails appear to come from legitimate domains. When recipient servers reject these forged emails, the bounce message is directed back to your domain. They recommend ensuring your domain has SPF, DKIM, and DMARC records properly set up to prevent this type of abuse and improve email deliverability.
21 Mar 2022 - Google Workspace Admin Help
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