How do URLs in newsletters affect email deliverability and what tools can assess URL reputation?

Key findings

• URL scrutiny: Mailbox providers assess the reputation of all URLs in an email, including redirect paths and the final destination. A single problematic URL can compromise an entire email's deliverability.
• Hidden risks: URL shorteners and third-party tracking links can obscure the true destination, posing a risk if the underlying domain has a poor reputation. Using your own owned tracking domains is generally preferred. You can learn more about this in our guide on how link shorteners impact deliverability.
• Reputation by association: Linking to domains with questionable or inconsistent reputations (like some news sites or affiliate partners) can negatively impact your sender reputation, even if your own sending practices are good.
• Tool limitations: Many publicly available URL checkers offer only superficial assessments, failing to provide the deep insights needed for deliverability-specific concerns. True reputation data is often proprietary to MBPs.
• Excessive links: An overly high number of links in an email can also trigger spam filters, regardless of their individual reputation. Quantity matters alongside quality.

Key considerations

• Ownership: If possible, use your own domains for all tracking and redirection within your emails. This gives you more control over the reputation associated with your links.
• Transparency: Avoid excessive or unnecessary redirects. Ensure that the visible URL in your email aligns with the landing page domain to build trust with both users and filters.
• Vetting third-parties: Carefully vet any third-party domains you link to, especially for affiliate programs or shared content. Be aware that their reputation can become your problem.
• Holistic view: URL reputation is just one piece of the deliverability puzzle. Combine URL checks with overall sender reputation monitoring, content analysis, and engagement metrics to get a complete picture. You can learn about other factors in our guide on why emails fail.

Key opinions

• Frustration with tools: Marketers frequently express frustration with readily available URL reputation tools, as they often provide vague 'safe' statuses without explaining how a link might influence inboxing.
• Difficulty in pinpointing: It is challenging to isolate a single problematic URL when many links (e.g., to news sites, affiliates) are widely used by both good and bad actors, making A/B testing or root cause analysis difficult.
• Redirect path concerns: Marketers are suspicious that not just the final destination URL, but also domains within a redirect path, could be influencing deliverability.
• Impact of external domains: Every external domain linked to in an email has its own reputation, and marketers acknowledge they implicitly take on that reputation risk.

Key considerations

• Affiliate program review: For those with affiliate programs, regularly audit the domains used by affiliates, as their practices can directly impact your sender reputation. Consider reviewing our guide on URL shorteners and domain reputation.
• Internal click tracking: If not already implemented, use your own domain for click tracking to avoid reliance on third-party domains whose reputations you cannot control.
• Contextual analysis: Beyond just links, consider the overall context of your email content. Spam filters evaluate the entire message, including text and image reputation. Learn more about how to evaluate email health with our email deliverability tester.
• Engagement metrics: Monitor engagement rates (opens, clicks, unsubscribes, spam complaints) closely for emails with varying link profiles to identify patterns. Consistent low engagement or high complaints can signal issues, even if direct blocklistings aren't evident.

Key opinions

• MBP-centric reputation: True URL reputation data resides primarily with mailbox providers, making it challenging for senders to fully ascertain their links' standing. Public tools offer limited insight (for example, refer to the SpamResource website for more detailed explanations of this principle).
• Redirect path visibility: Tools like URLScan.io are recommended for gaining visibility into full redirection paths, which is crucial for identifying intermediate domains that could have a negative reputation.
• Domain ownership benefits: Using an owned domain for click tracking and redirects significantly mitigates deliverability risks associated with third-party URLs. This practice puts reputation control back in the sender's hands. More on this can be found in our guide about determining if third-party links affect deliverability.
• Statistical analysis: Applying statistical models (e.g., multiple regression) to newsletter performance data can help identify which specific domains are consistently linked to lower bounce or click rates, offering a data-driven approach to URL vetting.

Key considerations

• Proactive vetting: Regularly vet all external domains in your emails for potential malicious use or associations with bad actors. This is especially important for domains in affiliate programs or publicly accessible content.
• Monitor blocklists: While blocklists (or blacklists) might not always show individual URL reputations, monitoring for your own domain or IP on blocklists can indicate broader reputation issues that could be linked to your outbound URLs. You can check your status with our blocklist checker.
• Educate senders: It's crucial to educate marketing teams on the importance of link reputation and the technical implications of different URL structures (e.g., direct links vs. tracked links) on deliverability.
• Use comprehensive tools: Supplement basic URL checkers with security analysis tools (like VirusTotal.com) to uncover deeper issues that traditional reputation services might miss. These tools offer more granular data on potential threats associated with URLs, helping to prevent your emails from being flagged for security reasons.

Key findings

• URL structure and encoding: Technical documentation (e.g., RFCs) specifies how URLs should be structured and encoded. Deviations can lead to parsing errors or flags from spam filters. You can read more about this in our article on unencoded URLs and deliverability.
• Malicious content detection: Mailbox provider guidelines consistently state that identifying and blocking URLs associated with malware, phishing, or other abusive content is a top priority for protecting users.
• Redirect chain scrutiny: Security documentation highlights that redirects are a common vector for malicious activity. All intermediate domains in a redirect chain are assessed for reputation and potential threats. See our guide on how link redirects affect deliverability.
• HTTPS importance: Industry best practices emphasize the use of HTTPS for all linked resources to ensure secure data transmission and build trust. Non-HTTPS links may be viewed with suspicion by modern filtering systems (e.g., from Salesforce documentation on deliverability).

Key considerations

• Adhere to standards: Ensure all URLs in your emails strictly follow RFC standards for proper formatting and encoding to avoid being flagged as malformed.
• Use secure links: Prioritize HTTPS for all links, including tracking and images. This signals trustworthiness to MBPs and recipients.
• Avoid known bad actors: Regularly consult public threat intelligence feeds or security reports to identify domains with a history of malicious activity and avoid linking to them. This directly impacts how your email is perceived by blocklists (or blacklists), as explained in our guide on email blacklists.
• Monitor postmaster tools: Leverage tools like Google Postmaster Tools, which provide feedback on URL and domain reputation metrics based on their internal filtering. This can offer direct insight into how your links are perceived by major mailbox providers. You can get started with our ultimate guide to Google Postmaster Tools.