Why is my AWS hostname blacklisted in Abusix and how do I resolve it?
Michael Ko
Co-founder & CEO, Suped
Published 16 May 2025
Updated 19 Aug 2025
5 min read
Dealing with an AWS hostname blacklisted in Abusix can be a puzzling experience, especially if you're primarily using AWS S3 for hosting email images. A common bounce message indicating a block on mybrand.s3.amazonaws.com by a blocklist like dblack.abusix.fslupdate.com can leave you wondering if the problem is specific to your usage or a broader issue with Amazon's infrastructure. It is critical to understand why this happens and what steps you can take to mitigate the impact on your email deliverability.
This situation often arises because dblack is designed to list hostnames that appear within the body of an email message, not necessarily the sending IP. While your emails might be sent through a reputable ESP like Pardot, if the content contains links to blacklisted AWS S3 hostnames, your messages can still be blocked. Let's delve into the root causes and effective solutions.
Abusix is a well-known provider of threat intelligence, including various blocklists that email service providers use to filter out unwanted mail. Their dblack (domain blacklist) specifically targets domains and hostnames that are observed in spam or malicious emails, particularly when they appear in the message body. This is distinct from IP address blacklists, as it focuses on the content linked within your email, rather than the sender's infrastructure.
The reason your AWS S3 hostname might be caught in this net, even if your direct sending practices are clean, often comes down to the shared nature of cloud hosting environments. Public cloud services, like Amazon Web Services, are unfortunately attractive to spammers and malicious actors due to their ease of access and scalability. When bad actors host abusive content or launch spam campaigns using S3 buckets, their activity can lead to a broad blocklisting (or blacklisting) of s3.amazonaws.com and its subdomains.
This can manifest as a wildcard listing, meaning any hostname under *.s3.amazonaws.com could be blocked. Even if s3.amazonaws.com isn't listed directly on Abusix's lookup portal, a specific subdomain related to your bucket, like mybrand.s3.amazonaws.com, could be. This is a common challenge for legitimate senders leveraging popular cloud services.
Why your AWS S3 hostname gets caught
While your specific content or sending practices may be pristine, your images or other hosted assets are being delivered from a hostname (and underlying IP range) shared with countless other AWS users. Some of these users inevitably engage in abusive practices, leading to the entire shared resource being blacklisted (or blocklisted).
Email systems that consult Abusix's dblack list will then flag any email containing links to these blacklisted hostnames, regardless of the sender's primary domain or email reputation. This means your legitimate emails, containing essential images hosted on AWS S3, might be rejected or sent to spam folders.
The shared infrastructure dilemma
When you use generic hostnames provided by public cloud services like Amazon S3, you inherit the reputation of the entire shared network. Unlike dedicated IPs or custom domains, you have less control over the actions of other users who might be sharing the same underlying infrastructure. This exposure can lead to your legitimate assets being flagged due to the actions of unrelated third parties.
Practical steps to resolve the issue
The most effective way to resolve this issue and prevent future blacklistings of your AWS hostnames is to avoid using generic Amazon S3 hostnames directly in your email content. While you can continue to host your images on S3 for storage, you should serve them through a custom domain that you control. This allows you to build and maintain a unique reputation for your assets, independent of Amazon's shared infrastructure. If you're encountering widespread email blocklist issues, it is useful to review your overall email infrastructure.
Current approach: using generic AWS S3 hostnames
Your emails include links to images like mybrand.s3.amazonaws.com/image.jpg. This exposes your email content to the shared reputation of s3.amazonaws.com, increasing the risk of being blacklisted by services like Abusix dblack. While it offers simplicity, it compromises your deliverability control.
Recommended approach: custom domain for images
Instead of direct S3 links, set up a custom subdomain like images.yourdomain.com and point it to your S3 bucket using a CNAME record. Your email links would then look like images.yourdomain.com/image.jpg. This gives you full control over the hostname's reputation, isolating it from general AWS S3 abuse.
Example CNAME Record for S3 Static Website HostingDNS
Beyond addressing the immediate blacklisting (or blocklisting), it is essential to implement proactive measures to safeguard your email deliverability. This includes consistent monitoring of your sender reputation and ensuring all elements of your email infrastructure are configured correctly. Staying informed about your domain's status on various blacklists is a continuous effort.
Email authentication: Always ensure your emails are properly authenticated with SPF, DKIM, and DMARC. While this specific Abusix issue is content-based, strong authentication builds overall sender trust.
Content best practices: Regularly review your email content for suspicious links, excessive images, or other elements that might trigger spam filters or blocklists. Using custom domains for all linked assets is a key step.
Engagement monitoring: Monitor your email engagement metrics, such as open rates, click-through rates, and complaint rates. Low engagement or high complaints can negatively impact your sender reputation, increasing the likelihood of being blacklisted (or blocklisted).
Do
Don't
Host images on a custom subdomain (e.g., images.yourdomain.com).
Directly link to s3.amazonaws.com or similar generic cloud hostnames.
Ignore bounce messages and deliverability reports.
Continuously monitor your domain and IP reputation on major blocklists.
Include sensitive or suspicious links in your email content.
Views from the trenches
Best practices
Always host images and assets on a custom subdomain (e.g., images.yourdomain.com) for better control over reputation.
Regularly check your primary sending domains and any linked hostnames against major blocklists.
Ensure your email authentication protocols, including SPF, DKIM, and DMARC, are correctly configured.
Monitor email engagement metrics to catch potential deliverability issues early.
Common pitfalls
Directly linking to generic AWS S3 hostnames in email content, inheriting the reputation of shared cloud infrastructure.
Assuming that only your sending IP or primary domain can be blacklisted, overlooking content-based blocklists like Abusix dblack.
Ignoring bounce messages that indicate hostname blacklisting, which can lead to continued deliverability issues.
Not implementing a custom domain for images, which perpetuates reliance on shared, potentially problematic hostnames.
Expert tips
If a wildcard listing occurs, it indicates a broader issue with the shared infrastructure. Focus on migrating off the problematic hostname rather than just requesting delisting.
The recipient's ISP decides which blocklists to use; understanding their filtering policies can help mitigate issues.
While direct delisting requests might temporarily remove a specific hostname, the fundamental issue of shared reputation persists.
Leveraging CNAME records for custom subdomains ensures you retain hosting flexibility while gaining reputation control.
Expert view
Expert from Email Geeks says Abusix dblack is specifically for listing hostnames that appear within the body of an email message.
2020-07-14 - Email Geeks
Expert view
Expert from Email Geeks says it is highly recommended for any sender to ensure that no email they send contains anything with an AWS rDNS hostname in either the headers or the body.
2020-07-14 - Email Geeks
Securing your email's future
Being blacklisted on Abusix (or blocklisted) due to an AWS hostname in your email content is a clear signal that it is time to reassess how you host your email assets. While Amazon Web Services offers incredible convenience and scalability, its shared nature means that generic hostnames like s3.amazonaws.com can carry a higher risk of being flagged due to abuse by other users. By shifting to a custom domain for your email images and other linked content, you regain control over your online reputation and significantly enhance your email deliverability. Proactive monitoring and adherence to email best practices will ensure your messages consistently reach the inbox.
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technoirc.org
TechTheft
Amazon Web Services, are unfortunately attractive to spammers and malicious actors due to their ease of access and scalability. When bad actors host abusive content or launch spam campaigns using S3 buckets, their activity can lead to a broad blocklisting (or blacklisting) of s3.amazonaws.com and its subdomains.
Amazon S3, you inherit the reputation of the entire shared network. Unlike dedicated IPs or custom domains, you have less control over the actions of other users who might be sharing the same underlying infrastructure. This exposure can lead to your legitimate assets being flagged due to the actions of unrelated third parties.
s3.amazonaws.com or similar generic cloud hostnames.
