What is email content cloning?

Email content cloning (or clone phishing) is when attackers duplicate the content and design of a legitimate email and send it from an unauthorized, often malicious, domain. The purpose is usually to damage your brand's reputation, cause recipient confusion, or warm up new sending infrastructure for future malicious campaigns.

How can I identify if an email is a cloned attack?

The best way is to examine the full email headers. Look for the Return-Path , Received-SPF , and Authentication-Results fields, as these will reveal the true sender and if the email failed your domain's authentication checks.

What is the most effective technical defense against content cloning?

Implement DMARC with a p=reject policy. This tells receiving mail servers to reject emails that fail DMARC authentication and purport to be from your domain. Also, ensure your SPF and DKIM records are correctly configured.

What immediate steps should I take if my brand is targeted?

Begin by informing affected users that the emails are not from your company and provide clear instructions on what to do. Report the malicious domains to their hosting providers, and most importantly, strengthen your email authentication with DMARC to prevent future spoofing.

How to deal with email content cloning and reputational spam attacks? - Sender reputation - Email deliverability - Knowledge base

Email content cloning and reputational spam attacks are a growing concern for businesses. This happens when malicious actors duplicate legitimate emails, often with the same content and even links, and then send them to a large, unsolicited audience. While it may not always involve direct credential theft, the primary goal is to damage your brand's sender reputation and erode trust with your recipients.

The fallout can be severe, leading to increased spam complaints, blocklisting (or blacklisting), and significantly reduced email deliverability for your legitimate campaigns. Understanding the mechanisms behind these attacks and implementing robust defense strategies is crucial to protect your email program and brand integrity.

Understanding the attack: content cloning and replay

At first glance, an attack involving cloned email content might seem baffling, especially when the malicious emails retain your original links and branding. This is known as clone phishing. Unlike traditional phishing, where links are typically swapped for malicious ones, clone phishing can simply replicate your emails to send them to unwanted recipients. This still leads to complaints and a damaged sender reputation.

A key distinction to make is between simple content cloning and email replay attacks. Simple content cloning involves copying your email's HTML and text, then sending it from a different, often suspicious, domain. Email replay attacks are more sophisticated, typically involving the capture and re-sending of an authentic email, sometimes even attempting to replicate the original sender's address.

Content cloning

Mechanism: Spammers copy your email design and text without altering links.
Sender: Sent from a completely different, unrelated domain.
Impact: Causes recipient confusion, leading to spam complaints against your brand, even if your systems aren't compromised.

Email replay attacks

Mechanism: Malicious actors resend a legitimate, previously delivered email.
Sender: Often appears to come from your actual domain or a very close spoof.
Impact: Can directly affect your sender authentication and lead to blocklisting of your legitimate sending IPs and domains. Learn more about identifying email forging and replay attacks.

One possible motivation for these attacks, even if links aren't altered, is IP or domain warming. Spammers use recognizable, legitimate content to establish a positive sending history for their new or unknown IPs and domains. The high engagement (clicks on unsubscribe or consent links) from confused recipients helps them build a perceived reputation, which they can then leverage for more overtly malicious campaigns later. This makes it challenging to deal with, as the immediate indicators may not be outright malicious links.

Identifying the source of cloned emails

The most effective way to identify the true source of these cloned emails is by examining the full email headers. These headers contain a wealth of information about the email's journey from sender to recipient, including the originating IP address, authentication results (SPF, DKIM, DMARC), and routing paths. Without this forensic data, it is difficult to distinguish a genuine email from a cleverly cloned one.

Look for specific headers such as Return-Path, X-Originating-Ip, and the results of Received-SPF, Authentication-Results, and DMARC-Filter. These will reveal the true sender and if they passed your domain's authentication checks. In clone phishing, the From address may look like yours, but the Return-Path or Received headers will reveal the malicious domain.

Example of email headers from a cloned email attacktext

Received: from sender.maliciousdomain.com (malicious.ip.address.1) by receiver.yourdomain.com with ESMTPSA;
        Mon, 27 Apr 2025 00:00:00 +0000
Return-Path: <spoofed@yourdomain.com>
From: "Your Brand" <spoofed@yourdomain.com>
Subject: Your Legitimate Email Subject
Received-SPF: fail (yourdomain.com: domain of spoofed@yourdomain.com does not designate malicious.ip.address.1 as permitted sender)
Authentication-Results: mx.google.com; spf=fail smtp.mailfrom=spoofed@yourdomain.com;
 dkim=neutral (bad signature) header.i=@yourdomain.com; dmarc=fail (p=none dis=none) header.from=yourdomain.com

It can be challenging to obtain full headers from annoyed recipients, but it's essential. The header information will clarify whether it's a simple content clone from a third-party domain, or a more direct attempt at spoofing your domain. Once you have these headers, you can analyze them to identify the sender's actual infrastructure and potentially report them to their hosting provider.

The challenge of collecting email headers

Recipients who are frustrated by repeated spam may be reluctant to provide full email headers. This often means you’ll have to rely on the limited information they offer, making it harder to pinpoint the exact origin of the attack. Consider guiding them on how to get the full headers or provide a simpler reporting mechanism.

Mitigating reputational damage and preventing future attacks

Mitigating reputational damage and preventing future content cloning or spoofing attacks requires a multi-faceted approach. Implementing email authentication standards is paramount. DMARC, SPF, and DKIM work together to verify legitimate senders and instruct receiving mail servers on how to handle emails that fail authentication, including those with cloned content.

For clone phishing specifically, a DMARC policy set to p=reject or p=quarantine is your strongest defense. This instructs recipient mail servers to block or quarantine any email purporting to be from your domain that fails DMARC authentication. This directly combats the use of your brand in unauthorized emails, significantly reducing their impact. Consider transitioning your DMARC policy to quarantine or reject as soon as possible.

Here are key strategies to mitigate the damage and prevent future occurrences:

Immediate response: Inform affected users. Provide a clear, empathetic explanation that the emails are not from you and advise them not to interact with them. You can also add a message on your unsubscribe pages to address the issue directly, guiding users on what to do if they receive suspicious emails that appear to be from your brand. This helps mitigate damage from email spoofing.
Report abuse: If you identify the malicious domain or hosting provider (e.g., GoDaddy, as mentioned in the Slack thread), report the abuse. While spammers can quickly move to new domains, consistent reporting can make it harder for them to operate.
Enhance authentication: Ensure your SPF, DKIM, and DMARC records are correctly configured and enforced. DMARC is especially critical for instructing mailboxes to reject unauthorized emails from your domain. For more insights into how to prevent clone phishing, you can refer to Keepnet Labs' guide on clone phishing.
Monitor blocklists: Regularly check email blocklists (blacklists) to ensure your legitimate sending IPs and domains have not been inadvertently listed due to the attack.
Recipient engagement: Encourage legitimate recipients to mark unsolicited emails as spam only if they are truly spam, not just because they are annoyed by cloned content. Guide them to report abuse directly if possible.

Implementing DMARC with a strong policy is the most robust technical defense against email content cloning and spoofing. It ensures that only emails properly authenticated by your domain's SPF and DKIM records are delivered. This significantly reduces the ability of malicious actors to impersonate your brand effectively.

Authentication Method	Role in Preventing Cloning
SPF (Sender Policy Framework)	Authorizes specific IP addresses to send emails on behalf of your domain. If a cloned email comes from an unauthorized IP, SPF can cause it to fail. Microsoft, Yahoo, and other mail providers check SPF.
DKIM (DomainKeys Identified Mail)	Adds a digital signature to outgoing emails, verifying that the content hasn't been tampered with in transit. If spammers clone content and resend it, their DKIM signature will likely be invalid, leading to authentication failure.
DMARC (Domain-based Message Authentication, Reporting, and Conformance)	Builds on SPF and DKIM, telling receiving servers what to do with emails that fail authentication. A p=reject policy will ensure cloned emails that fail authentication are rejected outright, protecting your email domain reputation. Learn how to identify and handle spoofed emails.

Proactive measures and ongoing monitoring

Beyond technical configurations, ongoing vigilance and education are critical. Implement DMARC monitoring to receive daily reports on email authentication failures, which can alert you to potential spoofing or content cloning attempts. This allows you to see if your domain is being used by unauthorized senders and to adjust your DMARC policy accordingly.

Regularly check your sender reputation through blocklist monitoring services. Even with strong authentication, high spam complaint rates from cloned emails can still negatively impact your sending reputation. Educating your customers on how to identify legitimate emails from your brand, and what to do if they suspect a phishing or cloning attempt, can also reduce the impact of these attacks. A business protection guide to clone phishing emphasizes the importance of employee and customer awareness.

It’s also important to audit your unsubscribe process and landing pages. If spammers are using your legitimate unsubscribe links, it suggests they are either trying to generate clicks for warming, or to cause confusion and frustration. Consider adding a clear message on these pages indicating that if users received an unexpected email, it might be a spoofing attempt and offering guidance on how to report it.

Views from the trenches

Best practices

Ensure your DMARC policy is set to 'reject' to prevent unauthorized use of your domain in emails.

Regularly monitor your DMARC reports for signs of spoofing or unauthorized sending.

Educate your customer support team on how to identify cloned emails and guide users in reporting them correctly.

Add a clear message to your unsubscribe pages explaining how to deal with spoofed emails.

Common pitfalls

Not having a DMARC policy or having it set to 'none', allowing spammers to spoof your domain.

Ignoring spam complaints from cloned emails, as this still negatively impacts your sender reputation.

Failing to collect full email headers from affected recipients, which are crucial for investigation.

Underestimating the impact of perceived spam, even if it's not originating from your systems.

Expert tips

Actively analyze email headers from suspicious emails to pinpoint the true source and attack vector.

Consider engaging with domain registrars (like GoDaddy) and hosting providers where malicious domains are registered to report abuse.

Implement advanced spam filters that can detect lookalike domains and subtle spoofing attempts.

Cross-reference unusual traffic spikes on your unsubscribe or consent pages with reported spam incidents to track the attack's impact.

Expert view

Expert from Email Geeks says without understanding the full email headers and source, it's difficult to mitigate the attack, whether it's a replay, payload copying, or forwarding.

2025-04-24 - Email Geeks

Expert view

Expert from Email Geeks says if it is a replay attack, modifying the DKIM signing headers by adding more values can help oversign the original mail.

2025-04-24 - Email Geeks

Protecting your brand's email integrity

Email content cloning and reputational spam attacks pose a unique challenge, as they leverage your brand's trust to cause harm without necessarily compromising your systems directly. The key to combating these sophisticated attacks lies in a proactive and multi-layered defense strategy.

By rigorously implementing email authentication protocols like DMARC, actively monitoring your sender reputation and DMARC reports, and educating your users, you can significantly reduce the impact of these attacks. While completely stopping all malicious activity might be impossible, these measures ensure that your legitimate emails continue to reach the inbox, protecting your brand and maintaining recipient trust. This approach is essential for fixing deliverability issues and improving sender reputation.