Why is my AWS hostname blacklisted in Abusix and how do I resolve it?

Key findings

• Shared infrastructure: Listings often apply to entire subdomains like s3.amazonaws.com due to widespread abuse across various users on that shared platform. This is a common challenge with shared email infrastructure.
• dblack list: Abusix's dblack list specifically targets hostnames appearing within the body of email messages, which includes links to hosted images or other content.
• Wildcard listings: Even if your specific hostname isn't explicitly listed, a wildcard entry for *.s3.amazonaws.com can cause your emails to be blocked if they contain references to AWS S3. You can check the listing status of your domain on Abusix's website.
• Unforeseen impact: A delisting request for your specific AWS hostname might inadvertently delist a broader range of S3 subdomains, indicating a temporary or reactive policy by Abusix.

Key considerations

• Review email content: Identify all instances where your emails include links or references to shared AWS S3 hostnames, especially for images.
• Brand your assets: Instead of using the generic AWS S3 hostname, host images and other email assets on your own branded domain or a subdomain you control. This gives you more control over your email deliverability and sender reputation.
• Monitor blocklists: Regularly check blocklists (or blacklists) to understand how your sending practices and linked content are being perceived by anti-spam systems. This is part of maintaining good email deliverability.
• Understand recipient filters: Remember that while a blocklist operator like Abusix provides data, it is the recipient ISP that chooses to use that data to filter emails. Understanding their specific filtering mechanisms can be crucial for troubleshooting.

Key opinions

• Unexpected listings: Marketers are often surprised to find their emails blocked due to a shared hosting domain being blacklisted, especially when their own sending domains are clear.
• Confusion over scope: There's confusion about whether the blocklist (or blacklist) applies to their specific branded subdomain on AWS or to amazonaws.com in general.
• Historical usage: Some marketers have used S3 for years without issue, making recent blocklistings particularly perplexing.
• Impact on deliverability: The direct consequence is bounced emails, even if the primary sending domain (e.g., via Pardot) is reputable. This highlights the importance of addressing deliverability issues.

Key considerations

• Avoid generic hostnames: It is highly recommended to avoid embedding generic third-party hostnames (like s3.amazonaws.com) directly in email bodies for images or other assets.
• Host on owned domains: If remote images are necessary, host them on a subdomain of your own brand's domain (e.g., images.yourdomain.com). This allows for better control over reputation.
• Check subdomains and IPs: Marketers should use blocklist checkers for their primary sending domain and any domains or IPs referenced within the email body.
• Understand listing context: It is crucial to determine if a listing is for a specific subdomain or a broader wildcard, as this affects the resolution strategy. Abusix documentation often provides insights into common listing reasons.

Key opinions

• Wildcard application: Experts highlight that Abusix's `dblack` listing for Amazon S3 is likely a wildcard listing (e.g., *.s3.amazonaws.com), not specific to an individual user's bucket or domain. This means any subdomain on S3 could trigger a block.
• Reasonable policy: Many experts view a wildcard listing of shared domains like S3 as a reasonable measure by blocklist operators, given the volume of spam and malicious content often hosted on such platforms.
• Recipient ISP control: While Abusix provides the blocklist, the decision to use it for filtering rests with the recipient's ISP. This underscores that different ISPs may have varying levels of enforcement.
• Header and body scrutiny: Experts warn that even if the primary sending IP/domain is clean, any AWS rDNS hostname appearing in email headers or the body (like for images) can lead to filtering issues. This is a common pitfall in email deliverability.

Key considerations

• Host assets on owned domains: The primary recommendation is to avoid using shared domains for email content. Instead, host images and other embedded elements on a domain that you fully control. This could involve setting up a CNAME record from your domain to the AWS S3 bucket.
• Evaluate blocklist impact: Senders should assess the impact of being listed on a specific blocklist. If the bounce rate is low and only affects a small number of recipients, the immediate fix might be less urgent than if it impacts a major recipient. However, proactive measures are always best for managing sender reputation.
• Monitor for wildcard listings: To verify a wildcard listing, experts suggest searching Abusix for several random subdomains of s3.amazonaws.com. If multiple arbitrary subdomains are listed, it confirms a wildcard block.
• Understand ISP decisions: The `fslupdate.com` domain in the bounce message implies a specific recipient ISP (or anti-spam vendor they use) is leveraging Abusix data, reinforcing that recipient policies are the ultimate filter. More details can be found on industry blogs like Word to the Wise.

Key findings

• Network management focus: Abusix documentation often points to the need for network providers (ASN owners) to announce their abuse@ role address in their RIR WHOIS records, indicating a focus on the broader network's reputation rather than individual subdomains. This is highlighted in Abusix's network management troubleshooting guide.
• Intelligence and credibility: Abusix Intelligence provides insights into IPs and Domains, showcasing their reputation and credibility. A listing signifies a negative reputation score.
• Abuse patterns: Documentation suggests that blocklistings, especially for shared public cloud services, are often a response to observed patterns of spam or malicious content originating from those domains.
• Listing criteria: DNSBLs (DNS-based Blocklists), of which Abusix is one, typically list IP addresses, domains, and email addresses identified as sources or hosts of spam or malicious activity. More on this can be found in our guide to DNSBLs.

Key considerations

• Shared IP/domain risks: Documentation often implicitly or explicitly warns about the risks of using shared IPs or domains for email-related content, as the actions of one user can impact all others on the shared resource.
• Contacting the blocklist: When an AWS hostname is listed, contacting Abusix directly for delisting might be less effective than addressing the underlying issue of using a generic, shared hostname. For general Abusix delisting, see this guide.
• Proactive reputation management: Official best practices often recommend hosting all email-related content (including images, tracking pixels, etc.) on domains that are fully controlled and used solely by the sender, to isolate their reputation from broader network issues.
• Understanding listing types: Awareness of different blocklist types (IP-based, domain-based, DNSBLs like Abusix) and what they target (e.g., dblack for body hostnames) is crucial for accurate diagnosis and resolution, as detailed in various OSINT and threat intelligence resources.