How can I determine if third-party links in email affect deliverability?

Key findings

• No single reliable tool: There isn't one universal tool that can reliably determine if a third-party link has poor reputation across all mailbox providers.
• Provider-specific reputation: Link reputation is highly specific to each mailbox provider (ISP) and can vary greatly. What one system deems acceptable, another might flag.
• Content and context matter: The full URL path, domain reputation, and even the type of content on the linked page (e.g., a login page versus informative content) can influence how filters react.
• Dynamic and temporary rules: Some spam filter rules related to URLs are internal, temporary, and constantly updated, making comprehensive pre-check difficult.
• Shared domains risk: Link shortening services and shared content domains (like Dropbox or Google Drive) may inherently carry a higher risk due to their widespread use by both legitimate senders and spammers.

Key considerations

• Test emails: The most practical approach is to send test emails with and without the third-party links to various major mailbox providers. Monitor for noticeable changes in inbox placement. You can also use a tool for email deliverability testing.
• Domain reputation checks: While not definitive for all filters, check the linked domain against major URI blocklists or use tools like Google's Transparency Report for safe browsing status.
• Branded link tracking: If possible, wrap third-party links with your own branded link tracker (a custom subdomain), leveraging your sender domain's reputation rather than relying on the third-party's. Consider how URL shorteners and domain reputation interact.
• Reputable sources only: Prioritize linking to widely recognized and reputable sites. Be wary of domains with suspicious paths (e.g., wp-content that suggest a compromised site).

Key opinions

• Empirical testing is key: Many marketers rely on A/B testing, sending emails with and without the suspect links, to observe changes in deliverability. This provides direct, albeit reactive, insight.
• Shared link services are risky: Generic link shorteners or shared hosting domains are often flagged due to their common use by spammers, even if the content is legitimate. This is a common concern regarding link shortener impact on deliverability.
• Brand ownership matters: Leveraging your own branded domain for link tracking is preferred, as it allows your sender reputation to primarily influence the link's perceived safety rather than a third party's.
• Not always a major concern for good senders: If overall sending practices are high-quality, and the links aren't overtly spammy, minor link reputation issues might not significantly impact deliverability unless broader inboxing troubles are observed.

Key considerations

• Prioritize direct domain links: Strive to link primarily to your own domain (or branded subdomains) to maintain maximum control over your email's reputation. This also helps with the issue of third-party image or link hijacking.
• Monitor your overall deliverability: Don't isolate link issues. If you notice a sudden drop in inbox placement, investigate all potential causes, including link reputation. Our email deliverability test checklist can assist here.
• Leverage ESP features: If your email service provider (ESP) offers branded link tracking, utilize it. This can mitigate risks associated with shared or generic tracking domains.
• Assess link ubiquity: Highly common links (e.g., social media icons, Calendly) might have less impact, as their widespread use across both good and bad mail can dilute their individual reputational weight. MarketingSherpa suggests conducting test emails to see if inclusion causes deliverability problems.

Key opinions

• No reliable single source: Experts confirm that a truly reliable, comprehensive way to know if a third-party link will affect deliverability across all providers does not exist due to internal and temporary filter rules.
• Layered problems: There are multiple layers of potential problems, from URIs listed on public blacklists (blocklists) to specific URL patterns that individual spam filters might deem problematic.
• Machine learning influence: Spam filters extensively use machine learning, which learns from vast datasets. This means a link's impact can be highly contextual, dependent on other factors in the email and sender's history.
• Shared infrastructure risk: Certain widely used domains (e.g., Amazon S3, Dropbox, Google Drive) or even particular IP addresses hosting multiple domains can be prone to issues if one entity misbehaves.
• Content of linked page matters: The nature of the landing page, such as a simple login page versus rich content, can subtly influence how Google (and likely other ISPs) perceives the link's legitimacy.

Key considerations

• Leverage public security tools: For initial checks, consider running suspicious domains through tools like IBM's X-Force, Cisco's Talos, or VirusTotal to identify severe reputational problems or malware hosting. These can provide hints, though not guarantees.
• Observe delivery patterns: Send test emails containing only the suspect domain to multiple accounts across various providers. Analyzing the delivery patterns can give an indication of the domain's reputation and the severity of any issues.
• Content path inspection: Filters can get suspicious of specific URL paths, such as those pointing to wp-content or indicating cracked destinations. Always verify linked content.
• Understand domain ownership: Owning your own infrastructure (e.g., dedicated IP, custom tracking domains) offers more control over your deliverability, as fewer external factors can negatively impact it. This relates to how your email tool affects deliverability.
• Affiliate network CNAMEs: Be cautious when URLs use CNAMEs to redirect to affiliate networks, as these are frequently associated with spam and can trigger filters.

Key findings

• Linked domain reputation is key: The reputation of the domain a link points to is a primary factor influencing how it affects spam classification. Linking to disreputable or blacklisted (blocklisted) domains is highly problematic.
• Content quality extends to links: If email content is supported by a third-party, their reputation is factored into the email's overall reputation score.
• Number and type of links: The frequency of links within an email and whether they are redirects (especially to affiliate networks) can also influence spam scores. Too many links or suspicious redirects can be flagged, as highlighted in how multiple or long links affect deliverability.

Key considerations

• Only use reputable sites: Documentation often advises that if third-party sources must be used, they should only be widely recognized and reputable sites.
• Check linked domains: Before sending, check the domains of any third-party links. Some sources explicitly suggest using tools (like Google's Transparency Report) to verify link safety.
• Impact of poor third-party reputation: If third-party reputations are poor, or if the content they support is spammy, it can negatively impact the overall weight of your email's score and lead to deliverability issues.