How can I determine if third-party links in email affect deliverability?
Michael Ko
Co-founder & CEO, Suped
Published 28 Jul 2025
Updated 16 Aug 2025
7 min read
Email deliverability is a complex beast, and one area that often raises questions is the impact of third-party links. Many factors contribute to whether your email lands in the inbox or the spam folder, and the domains you link to are certainly on that list. Understanding how these external links influence your sender reputation and overall deliverability is crucial for any email sender.
The challenge lies in the fact that there isn't one single, universally reliable way to get a definitive score or a clear yes or no answer for every third-party link. Internet Service Providers (ISPs) and mailbox providers maintain their own proprietary systems and algorithms to assess domain and IP reputation, and these are constantly evolving.
The challenge of assessing third-party link reputation
When you include a link to an external domain in your email, you are essentially vouching for that domain's reputation. If the third-party domain has a poor reputation, it can negatively reflect on your own sender reputation, even if your sending practices are otherwise stellar. This is because email filters scrutinize all elements of an email, including its content and the reputation of linked domains, to determine its legitimacy.
The challenge with assessing third-party link reputation lies in the variability among different email providers. A domain considered perfectly fine by one provider, like gmail.com, might be flagged as suspicious by another. This lack of uniformity means there's no single, public database that definitively tells you a link's global reputation. It's a dynamic and provider-specific assessment.
This complexity is a core reason why understanding email deliverability is so crucial. It's not just about what you send, but also where your links lead. Poorly reputed links can trigger spam filters, leading to reduced inbox placement and lower engagement with your emails.
The inherent risks of third-party links
Reputation inheritance: Your sender reputation can be negatively impacted by the reputation of linked domains, even if they're not directly your own. Mailbox providers assess the overall weight of your email score based on all content within it.
Spam trigger: Third-party links, especially those associated with suspicious activity or frequently used by spammers, are common triggers for spam filters.
Dynamic assessment: ISPs constantly update their filters using machine learning, meaning a link that was fine yesterday might be problematic today due to new spam patterns.
Factors that influence link reputation
Certain types of third-party links are more likely to raise red flags with email filters. These often include domains associated with past spam campaigns, malware, or phishing attempts. Spam filters are designed to be suspicious of anything that looks like it could be trying to hide its true destination or intent.
Common culprits include generic link shortening services, especially those without custom domains. Spammers frequently use these to disguise malicious URLs. Additionally, links to shared content domains, such as dropbox.com or drive.google.com, can sometimes be viewed with suspicion because they are commonly abused by bad actors. Links that redirect to affiliate networks or those with paths indicating compromised websites (like 'wp-content' in unexpected contexts) also raise alerts.
It's also worth noting that the content of the landing page matters. I've seen deliverability issues arise when a link leads to a generic login page instead of actual content, even on a reputable domain. Mailbox providers want to see legitimate, valuable content at the destination of your links.
Higher risk links
Generic URL shorteners: Like bit.ly without a custom domain, as they are often used by spammers. Learn more about Bitly links and deliverability.
Shared content domains: Such as drive.google.com or dropbox.com, particularly if the files hosted are suspicious.
Compromised sites: Links to domains showing signs of being hacked, like unusual wp-content directories.
Lower risk links
Branded URL shorteners: Custom short domains that align with your brand, signaling legitimacy.
Reputable platforms: Links to well-known social media sites such as facebook.com or linkedin.com, due to their high volume of legitimate traffic. However, consider if TikTok links in email footers affect deliverability.
Content-rich pages: Landing pages with clear, valuable information, not just login forms.
Practical steps to assess link impact
Since direct reputation scores are hard to come by, the most effective way to determine if a third-party link affects deliverability is through controlled testing. This involves sending emails both with and without the suspicious link and observing the delivery patterns. You can also use seed list testing to see how your emails land across various mailbox providers.
For specific messages you're concerned about, you can check public URI blacklists (or blocklists) that list domains known for spamming or hosting malware. While not a complete picture, these lists can provide hints of severe reputational problems. You can also utilize resources like Google's Transparency Report to check link reputation for some insights.
Another strategy is to "wrap" third-party links with your own branded link tracker. This means the link visible in the email and clicked by the recipient belongs to your domain, which then redirects to the actual third-party site. This allows your domain's reputation to be the primary factor assessed by the ISP, rather than the third-party domain itself. This is especially useful for understanding how tracking links affect deliverability.
However, the link tracker must use your own domain, not a generic one, to be effective. For example, if you're sending from yourdomain.com, your tracking link should look something like links.yourdomain.com/unique-id. This maintains consistent branding and leverages your established domain reputation.
The best defense against third-party link issues is to minimize their use and, when necessary, to only link to highly reputable sources. If you must use third-party links, aim for well-known and trusted platforms with established positive reputations.
If you are using an Email Service Provider (ESP), leverage their branded link tracking features. Most reputable ESPs offer this, allowing you to route all links through a subdomain of your own, thereby retaining control over the link's perceived reputation. This is especially important as third-party emails linking to your website might get rejected.
While shared IP addresses or entry-level ESP solutions might seem like they leave you vulnerable, many domain blocklists (or blacklists) try not to list general ESP shared domains because they understand they are used by many different senders. However, owning your own infrastructure or ensuring your ESP offers dedicated domains and branded link tracking provides the most control and reduces external interference with your deliverability.
Ultimately, if your overall sender practices are high-quality, and the third-party link is not egregiously spammy, you're less likely to encounter significant issues. The link's reputation is just one data point among many that ISPs consider. If you start seeing signs of deliverability trouble, then it's time to investigate your links more closely.
Views from the trenches
Best practices
Always strive to link to your own domain in messages to reduce overall deliverability risks.
Use your Email Service Provider's (ESP) branded link tracking features whenever possible, configured with your own domain.
Send test emails with and without third-party links to observe any noticeable differences in delivery patterns.
Common pitfalls
Relying on generic URL shorteners without custom domains, as they are frequently used by spammers.
Linking to shared content domains like Dropbox or Google Drive if the content is unusual or unverified.
Ignoring the content of linked landing pages, especially if they are generic login pages without actual content.
Expert tips
Check public URI blacklists (blocklists) and ad blockers for hints of severe reputational problems with domains.
Be aware that mailbox providers maintain internal rules and reputations that are not publicly available.
Consider that the impact of a link can vary by IP range, even for the same link.
Marketer view
Marketer from Email Geeks says there isn't a single, reliable way to determine if third-party links have a poor reputation and affect deliverability.
2022-04-13 - Email Geeks
Expert view
Expert from Email Geeks says you can get hints by checking URI blocklists, ad blockers, and SpamAssassin rules, but many rules are internal to mailbox providers and can be temporary.
2022-04-13 - Email Geeks
Final thoughts on link reputation and deliverability
Determining the exact impact of third-party links on email deliverability is rarely a clear-cut process. It involves navigating the nuanced and often opaque reputation systems of various mailbox providers. While there's no single tool to give you a definitive answer, understanding the factors that influence link reputation can guide your strategy.
By prioritizing branded link tracking, being mindful of the reputation of external domains, and conducting controlled testing, you can proactively mitigate risks. Ultimately, maintaining a strong overall sender reputation through consistent good practices remains your most powerful asset in ensuring your emails reach their intended audience, regardless of the links they contain.
gmail.com, might be flagged as suspicious by another. This lack of uniformity means there's no single, public database that definitively tells you a link's global reputation. It's a dynamic and provider-specific assessment.
dropbox.com or 
drive.google.com, can sometimes be viewed with suspicion because they are commonly abused by bad actors. Links that redirect to affiliate networks or those with paths indicating compromised websites (like 'wp-content' in unexpected contexts) also raise alerts.
facebook.com or 
linkedin.com, due to their high volume of legitimate traffic. However, consider if TikTok links in email footers affect deliverability.
