When third-party emails linking to your website are rejected by Internet Service Providers (ISPs), it signals a potential issue with how your domain is perceived within those specific email contexts, even if your in-house emails perform well. This problem often arises due to discrepancies in link handling or reputation assessment tied to the sending domain versus the linked domain.
Key findings
Link reputation: Even if your main sending domain has a strong reputation, the inclusion of your site's links in emails from a third-party sender can be impacted by the third party's sender reputation.
Mismatched domains: Discrepancies between the visible link text and the actual HTML link (e.g., using a CNAME for tracking or a 'fake' URL structure within a real URL) can trigger fraud warnings and rejections.
Spoofing concerns: ISPs may interpret certain linking patterns from third parties as attempts at spoofing, even if the domain itself isn't directly spoofed.
Blocklist impact: While your main domain might not be on a blocklist (or blacklist), the third-party sender's IP or domain could be, leading to rejections for any email they send, including those linking to you. This can be complex, as explained in our guide to how email blacklists actually work.
ISP-specific filters: Some ISPs, like Comcast or CenturyLink, might have unique filtering rules that flag specific link structures or sender-to-linked-domain relationships as suspicious.
Key considerations
Review link structure: Work with third parties to ensure the structure of links to your site is clear and consistent, avoiding nested or obfuscated URLs. The domains in the visible text and the HTML should ideally match.
Monitor partner reputation: Understand that your domain reputation, while strong, can be affected by the reputation of domains sending emails that link to you. It's crucial to ensure your partners maintain good email sending practices.
Check for blocklistings: Confirm whether the third-party sender's IP or domain is listed on any major blocklists, as this could be the primary cause of rejection, as highlighted by Twilio's blog on email delivery failures.
Communicate with ISPs: If rejection messages explicitly state a filter on your domain, reach out to the postmaster of the affected ISP for clarification. This can often provide specific insights into their filtering mechanisms.
Utilize DMARC: Proper DMARC monitoring can help you understand authentication failures and potential spoofing attempts related to your domain, even when originating from third parties.
What email marketers say
Email marketers grappling with third-party email rejections often highlight the distinction between internal sending practices and those of partners. They tend to focus on the immediate, observable symptoms like bounce messages and the visual presentation of links, suggesting that even minor inconsistencies can trigger ISP filters designed to detect deceptive practices.
Key opinions
In-house vs. third-party: There's a common observation that in-house emails to one's own list rarely encounter rejections when external partners, even reputable ones, send emails linking to the same site.
Visual and HTML link mismatch: Marketers often suspect that a mismatch between the displayed link text (e.g., promotiondomain.com) and the actual underlying HTML link (e.g., partnerdomain.com/trackingstuff) can lead to fraud warnings from ISPs, as noted by MarketingSherpa.
Suspicion of unusual URL structures: Some marketers suspect that unconventional URL patterns, like corporation.com/corporate-partners/partner-com, where a domain-like string appears within a path, might be flagged by filters.
Direct domain filtering: Postmaster notes explicitly filtering a specific website domain, rather than an IP or sender, indicate that the issue is directly related to the linked content itself, not just the sender's reputation.
Key considerations
Obtain full email headers: To diagnose issues accurately, marketers should request the full email (including headers) from the third party, especially for the rejected messages. This helps in understanding the path and authentication status of the email.
Test partner emails: Even if a partner seems legitimate, testing their emails with your domain links through various email sending best practices (like using an inbox placement tester) can provide immediate insights into deliverability issues.
Review CNAME usage: If the third party uses CNAMEs for link tracking, ensure these are configured correctly and do not create deceptive link appearances that could be mistaken for spoofing.
Address unusual link patterns: Advise partners to simplify link structures. Avoid patterns that resemble domain names within subdirectories, such as domain.com/partner-com, as these can mimic phishing attempts.
Marketer view
Email marketer from Email Geeks observes that even when Corporation A's internal, high-volume email sends are successful, emails sent by their legitimate partners linking to Corporation A's website are frequently rejected. This indicates a specific issue with how third-party-linked content is being evaluated.
07 Nov 2018 - Email Geeks
Marketer view
An email marketer from Email Geeks explains that the postmaster's rejection note explicitly stated the filter was for 'website.com', not due to a spoofing attempt. This specificity, they note, makes the situation more puzzling, suggesting the linked domain itself is the problem.
07 Nov 2018 - Email Geeks
What the experts say
Email deliverability experts often delve into the technical underpinnings of why third-party emails linking to your domain might be rejected. Their insights typically focus on the nuances of email authentication, domain reputation, and how ISPs perceive the relationship between the sender's domain and any linked domains within the email content.
Key opinions
Spoofing detection: Experts suggest that ISPs like Comcast might flag emails containing links to an external domain as a spoofing attempt, particularly if the sender's reputation is not aligned with the reputation of the linked domain. This relates to how DMARC verification failures can occur.
CNAME and link tracking risks: The use of CNAMEs for link tracking can sometimes be misinterpreted by spam filters if not configured or presented carefully, leading to rejections.
Phishing pattern recognition: Specific URL patterns, like those resembling domain-com instead of .com, have historically been associated with phishing attempts and can trigger automated filters, even if legitimate in context.
Domain vs. IP blocklisting: An email's rejection can be due to the sending IP being on a blocklist rather than the linked domain, but some blocklists (or blacklists) also list domains, adding another layer of complexity to troubleshoot. Our comprehensive guide to email blocklists provides further detail.
Key considerations
Domain alignment: Ensure that the domain used for sending the email (the 'From' address) is properly authenticated (SPF, DKIM, DMARC) and aligns with the domains included in the links, especially when tracking redirects are involved.
Link structure transparency: Advise third-party senders to use clear, unambiguous link structures. Avoid practices that might obscure the true destination of the link or create visual confusion for recipients and filters.
Proactive monitoring: Regular blocklist monitoring for both your domain and any partner domains can help identify issues before they severely impact deliverability.
Postmaster engagement: If an ISP explicitly states a filter on your domain, direct communication with their postmaster team is the most effective way to understand the specific reason for the rejection and work towards resolution. This is often necessary to troubleshoot issues like email delays or blocks by ISPs.
Expert view
An email deliverability expert from Email Geeks suggests that Comcast might be perceiving third-party emails with links to Corporation A's site as a spoofing attempt. This highlights how ISP filters can interpret legitimate linking as suspicious activity.
07 Nov 2018 - Email Geeks
Expert view
An expert from Email Geeks questions whether a CNAME is being used with link tracking by the third-party sender. This implies that CNAME configurations can play a role in how ISPs evaluate the legitimacy of links within emails.
07 Nov 2018 - Email Geeks
What the documentation says
Official documentation and technical guides from email service providers and anti-spam organizations often outline the criteria for email rejection, including factors related to linked content. These resources typically emphasize sender reputation, authentication protocols like SPF, DKIM, and DMARC, and adherence to content policies to prevent emails from being flagged as malicious or spam.
Key findings
Domain and IP blocklisting: Documentation confirms that if a sender's IP address or domain is listed on a blocklist (or blacklist) by an email service provider or anti-spam organization, emails from that sender may be rejected or filtered. This is a common cause of email bounces.
Reputation and content linkage: Email deliverability troubleshooting guides often mention that all domains included in an email message, including those in hyperlinks, contribute to the overall reputation assessment of the email. A poor reputation for any included domain can negatively impact deliverability.
Fraud and phishing indicators: Technical documentation on email security frequently identifies mismatched visible and actual URLs as a common tactic in phishing. Filters are designed to detect such discrepancies, which can lead to rejections even if the linked domain is legitimate.
Authentication standards: Adherence to email authentication protocols like DMARC, SPF, and DKIM is critical. Documentation often emphasizes that these protocols help ISPs verify the sender's legitimacy and prevent spoofing, which indirectly affects how linked content is perceived.
Key considerations
Audit third-party link practices: Review how third parties construct and embed links to your website. Ensure they avoid obfuscation, excessive redirects, or misleading anchor text that could trigger spam filters.
Maintain domain reputation: Even when linking externally, your domain's reputation is paramount. Any association with problematic senders or content can impact your own deliverability. Understanding your email domain reputation is key.
Ensure authentication for all domains: If the third party is sending emails on your behalf or using your domain in any sender-related field, ensure all necessary authentication (SPF, DKIM, DMARC) is correctly implemented for their sending infrastructure to align with your domain.
Consult ISP postmaster guides: Major ISPs provide specific guidelines for senders. Regularly reviewing these, such as Google's or Microsoft's postmaster tools and documentation, can offer direct insight into their filtering policies, including those related to external links.
Technical article
Documentation from Twilio advises that if your IP address or domain is blocklisted by email service providers or anti-spam organizations, your emails may be rejected or filtered out. This underscores the fundamental impact of blocklist status on email delivery, even when linking to reputable sites.
04 May 2022 - Twilio
Technical article
Abusix documentation on email bounces often attributes them to the sender's IP being blocklisted. This means that if the third-party sending the email is on a blocklist, all emails from them, including those with legitimate links, are likely to bounce.