Why am I receiving bounce messages for emails I didn't send from my domain?
Matthew Whittaker
Co-founder & CTO, Suped
Published 26 Apr 2025
Updated 19 Aug 2025
8 min read
It can be quite alarming to discover your inbox flooded with bounce messages for emails you never sent. This phenomenon, often leading to confusion and concern, suggests that your domain's email address is being misused by unauthorized third parties. It's a common issue in the email security landscape, primarily stemming from a tactic known as email spoofing.
These unexpected bounces are typically a byproduct of spam campaigns where cybercriminals forge sender addresses to disguise their true identity. When these forged emails are sent to non-existent or problematic recipient addresses, the bounce notifications, or "backscatter" spam, are inadvertently routed back to your legitimate domain, creating a deluge of unwanted mail in your inbox.
Understanding email spoofing and backscatter
Email spoofing is the act of forging an email header to make the message appear as though it originated from someone or somewhere other than the actual source. Spammers do this because it allows them to hide their real identity and bypass basic spam filters. By using your domain, they leverage its perceived legitimacy to trick recipients into opening malicious or unsolicited emails. The reason you receive the bounce messages is because, while the email appears to come from your domain, it was actually sent from another server entirely. When that email fails to deliver (e.g., to an invalid recipient address), the bounce message is sent to the listed sender, which is your domain.
This leads to what is known as backscatter spam. When spammers send out large volumes of emails using a forged sender address (your domain) to a broad list of recipients, many of these recipients' email addresses will inevitably be invalid or non-existent. The mail servers of these invalid recipients will then attempt to send a bounce notification back to the sender listed in the "From" header, resulting in these bounce messages landing in your inbox. This isn't a sign that your server has been compromised or is sending the emails, but rather that your domain has been picked at random, or perhaps it was harvested from a list, and is being used as a decoy.
While email spoofing is the primary cause, receiving these bounce-back messages when you haven't sent emails is specifically a symptom of backscatter spam. You can learn more about this issue directly from the source by checking articles about receiving returned emails you didn't send. Another authoritative source describes bounce back and backscatter spam.
The technical reasons behind the bounces
The good news is that these bounces don't necessarily mean your email system has been compromised. The ability for spammers to use your domain in the "From" address without actually sending mail through your servers is due to the inherent nature of the SMTP protocol, which doesn't originally verify the sender's identity. This is why email authentication protocols were developed.
To combat spoofing and ensure legitimate emails are delivered, mechanisms like SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance) are crucial. SPF verifies that emails from your domain are sent from authorized servers. DKIM uses cryptographic signatures to ensure the email hasn't been tampered with. DMARC ties these two together, providing instructions to receiving mail servers on how to handle emails that fail authentication. For a more detailed look into these, you can consult a simple guide to DMARC, SPF, and DKIM.
If these authentication protocols are not properly implemented for your domain, it becomes easier for spammers to spoof your email address, leading to these bounce messages. Ideally, a receiving server should reject spoofed mail at the connection level, preventing the bounce from ever being generated. However, not all servers are configured to do this, resulting in backscatter.
Ensuring proper authentication
Implementing a DMARC policy with a "reject" or "quarantine" setting is the strongest way to prevent email spoofing of your domain. While it won't stop the initial spoofed email from being sent by a third party, it instructs receiving mail servers, such as Google and Microsoft, to reject or quarantine any email that claims to be from your domain but fails DMARC authentication. This drastically reduces the amount of backscatter you receive.
Impact on your domain reputation
Although these bounce messages are not directly caused by your actions, a high volume of them can inadvertently affect your domain's reputation. Internet Service Providers (ISPs) and email providers monitor various signals to assess sender legitimacy, and a sudden surge in bounce messages originating from your domain, even if spoofed, might trigger their spam filters. This could lead to your legitimate emails being delivered to the spam folder or, in severe cases, outright rejected.
Your domain could also end up on an email blocklist (sometimes called a blacklist). If an ISP sees a large number of emails failing authentication and appearing to originate from your domain, they might consider listing your domain on a blocklist. Being listed on a blocklist can severely impact your email deliverability, as many receiving servers use these lists to block mail from known spam sources. Understanding what happens when your domain is put on a blocklist is essential for maintaining good email hygiene.
Monitoring your domain's reputation is key. You can check if your domain has been listed on any blocklists using a blocklist checker. If you find your domain listed, you'll need to follow the specific delisting procedures for each blocklist. Preventing the issue in the first place, however, is always the best strategy.
Steps to mitigate and prevent future issues
The most effective way to address the issue of receiving bounce messages for emails you didn't send is to implement and enforce email authentication protocols, especially DMARC. By deploying a DMARC policy, you tell receiving mail servers that emails from your domain should only be considered legitimate if they pass SPF or DKIM checks. This significantly reduces the likelihood of spammers successfully spoofing your domain.
Start by generating a DMARC record. A common starting point is a policy of "none" (p=none) to monitor traffic without affecting delivery, then gradually moving to "quarantine" (p=quarantine) or "reject" (p=reject) as you gain confidence. You can use a free DMARC record generator tool to create one. An example DMARC record might look like this:
Beyond DMARC, regularly monitor your email logs and bounce messages, including those from Gmail for any issues. This proactive approach helps you identify and resolve potential issues quickly. If your domain somehow gets listed on a blocklist or blacklist, you might experience emails being blocked by providers like Gmail, even if you're not the one sending the spam. Monitoring for blocklist (or blacklist) presence with blocklist monitoring can help you stay on top of your domain reputation.
Protecting your domain's reputation
Receiving bounce messages for emails you didn't send is a clear indicator that your domain is being targeted by spammers for spoofing or backscatter. While it can be frustrating, it's not an insurmountable problem. By understanding the underlying causes and implementing robust email authentication protocols like DMARC, SPF, and DKIM, you can significantly reduce the volume of these unwanted bounces and protect your domain's reputation.
Proactive monitoring of your DMARC reports (using a service for DMARC monitoring) and quickly addressing any authentication failures are crucial steps. This ensures that your legitimate emails reach the inbox while preventing malicious actors from abusing your domain, ultimately leading to a cleaner inbox and a stronger sender reputation.
Views from the trenches
Best practices
Always implement DMARC with a policy of at least p=quarantine to prevent unauthorized use of your domain.
Regularly monitor your DMARC reports to identify any unusual sending activity or misconfigurations.
Ensure your SPF and DKIM records are correctly set up and validated for all legitimate sending sources.
Common pitfalls
Ignoring unexpected bounce messages and assuming they are harmless, which can lead to reputation damage.
Not having a DMARC record, or having one with a p=none policy for too long, leaving your domain vulnerable.
Failing to monitor blocklists (blacklists) for your domain's presence, missing early warnings of reputation issues.
Expert tips
Use forensic reports from DMARC to identify the source of spoofed emails and report them to relevant authorities.
Consider implementing BIMI to further enhance brand trust and email security for your domain.
Regularly audit all services that send email on behalf of your domain to ensure they are properly authenticated.
Expert view
Expert from Email Geeks says a flood of bounces for emails you didn't send usually means someone is forging your addresses in their from line. They're not using your server, just your domain.
2019-06-19 - Email Geeks
Expert view
Expert from Email Geeks says spammers often make up random addresses and grab a domain to use, then send mail to non-existent recipients. The bounces go to the forged sender, which is you.
Google and 
Microsoft, to reject or quarantine any email that claims to be from your domain but fails DMARC authentication. This drastically reduces the amount of backscatter you receive.
Gmail for any issues. This proactive approach helps you identify and resolve potential issues quickly. If your domain somehow gets listed on a blocklist or blacklist, you might experience emails being blocked by providers like Gmail, even if you're not the one sending the spam. Monitoring for blocklist (or blacklist) presence with blocklist monitoring can help you stay on top of your domain reputation.
