Why does Gmail show a 'Suspicious Link' notification for HTTPS websites?
Matthew Whittaker
Co-founder & CTO, Suped
Published 29 Apr 2025
Updated 15 Aug 2025
9 min read
It can be perplexing when Gmail displays a 'Suspicious Link' notification for a website you know uses HTTPS, especially when the link appears perfectly normal. We typically associate suspicious warnings with insecure HTTP sites or obvious phishing attempts, so seeing one for a legitimate, encrypted link is quite alarming. This often leads to questions about how Gmail evaluates links and what might be going on behind the scenes.
Gmail's primary goal with these warnings is to protect its users from phishing, malware, and other malicious content. While HTTPS provides encryption for data in transit, it doesn't inherently guarantee the trustworthiness of the site itself. A malicious actor can still set up an HTTPS-enabled website for illicit purposes. Therefore, Gmail's security checks go far beyond just checking for an SSL certificate.
The issue often stems from various factors, including sender reputation, the domain's history, the nature of link redirects, or potential mismatches in how the link is presented versus its actual destination. It can be a nuanced problem that requires a deeper look into your email sending practices and infrastructure.
The puzzle of secure links and Gmail's evaluation
When you encounter a 'Suspicious Link' warning for an HTTPS site, it signifies that Gmail's sophisticated algorithms have identified something amiss, even if the site is encrypted. It's important to remember that a valid SSL certificate (and thus HTTPS) only confirms that the connection to the website is secure and encrypted, not that the website itself is benign or legitimate. Phishers and spammers frequently use HTTPS on their malicious sites to appear more trustworthy. For more details on why your messages might be flagged, you can refer to our guide on why emails get a phishing warning.
Beyond encryption, Gmail scrutinizes various aspects of the email and the linked content. This includes the sender's reputation, historical sending patterns, the content of the email, and the nature of the linked domain. If any of these elements raise a red flag, a warning may be issued. This is why legitimate emails sometimes trigger inconsistent suspicious link warnings.
Google also leverages its extensive Safe Browsing service, which identifies unsafe websites across the web. If the domain linked in your email has been flagged by Safe Browsing for malware, phishing, or unwanted software, Gmail will issue a warning regardless of whether the link uses HTTPS. Even if your site is clean, a previously compromised sub-domain or a shared IP on a blocklist (or blacklist) could trigger such alerts. You can learn more about how email blocklists work.
Common triggers for suspicious link warnings
Several factors can cause Gmail to flag an HTTPS link as suspicious. One of the most frequent culprits involves link tracking redirects. Many email service providers (ESPs) use custom tracking domains, often set up as CNAME records pointing to the ESP's infrastructure. If the SSL certificate for your custom tracking domain doesn't match the certificate of the ESP's domain that it redirects to, it can create a certificate mismatch error, which Gmail might interpret as suspicious activity.
Another significant factor is the sender's reputation. If your domain or sending IP address has a low sender reputation (or bad reputation) due to past spam complaints, low engagement, or being listed on a blocklist (or blacklist), Gmail is more likely to flag your emails and their links. This is a common reason for Gmail flagging messages as suspicious.
Shared sending environments, where multiple senders use the same IP addresses, can also contribute to the problem. If another sender on your shared IP has engaged in malicious activities, it can negatively impact the reputation of all senders on that IP, leading to warnings for otherwise legitimate links. This highlights the importance of choosing a reputable ESP.
Furthermore, Gmail may flag links if the displayed text of the link differs significantly from the actual URL it points to. While a common practice for clean link shortening or branding, this can be abused in phishing attempts. If Gmail perceives this as an attempt to deceive users, it will trigger a warning. Domains that are very new or not yet well-indexed by Google may also face challenges. Read more about unindexed domains being marked dangerous.
Cause
Description
Impact
Certificate mismatch
Your custom tracking domain's SSL certificate does not match the ESP's domain it redirects to, causing a browser error.
Users see a privacy error before reaching the final HTTPS destination.
Low sender reputation
Your sending domain or IP has a poor history with or is on a blocklist (or blacklist).
Emails are often flagged, sent to spam, or links are warned against.
Shared IP issues
Other senders on your shared IP are engaging in spammy or malicious behavior.
Your deliverability and link trust are negatively affected by others' actions.
Deceptive link text
The displayed link text significantly differs from the actual URL, perceived as cloaking.
Triggers warnings due to potential phishing indicators.
Diagnosing and mitigating the issue
To diagnose why Gmail is flagging your HTTPS links, start by verifying your domain's reputation using Google Postmaster Tools. This invaluable resource provides insights into your sending reputation, spam rate, and authentication errors, which are all crucial indicators of how Gmail perceives your email program. Any sudden drops in reputation could explain the new warnings.
Next, ensure your email authentication protocols are correctly configured. Strong implementation of SPF, DKIM, and DMARC is fundamental for establishing trust with mailbox providers, including Gmail. Misconfigurations can lead to Gmail marking emails as dangerous. A simple guide to these protocols can be found here. Additionally, manually inspect the URL of the suspicious link by hovering over it in the email (without clicking) to see the actual destination. If it's a tracking link, confirm that the SSL certificate for that specific tracking domain is valid and matches the intended hostname.
If the issue persists and appears to be related to link tracking, consider working with your ESP to ensure proper SSL configuration for your custom tracking domain. Some ESPs allow you to upload your own certificates or handle the certificate management for you. In some cases, if the issue is a consistent certificate error with the tracking subdomain, temporarily using HTTP for the tracking link and then redirecting to HTTPS on the landing page might bypass the immediate warning, though this is not a long-term solution for optimal security perception. For privacy errors, check our guide on why you get privacy errors.
Problem: Untrusted link tracking
When your custom tracking domain (e.g., links.yourdomain.com) uses a CNAME to point to your ESP's tracking server (e.g., tracking.esp.com), but the SSL certificate presented by tracking.esp.com doesn't cover links.yourdomain.com.
Certificate Mismatch: The browser sees a mismatch between the requested domain and the certificate's common name.
User Trust Impact: Causes 'privacy error' or 'suspicious link' warnings, eroding user confidence.
Solution: Proper SSL for custom domains
Ensure your ESP supports proper SSL certificate configuration for custom tracking domains. This might involve setting up a dedicated SSL certificate for links.yourdomain.com directly within the ESP's platform.
Dedicated SSL: Request or configure a specific SSL certificate for your custom tracking subdomain.
ESP Support: Work with your ESP's support team to implement this correctly.
Proactive measures to build trust
To prevent 'Suspicious Link' warnings in the first place, focus on building and maintaining a strong sender reputation. This includes consistently sending valuable, relevant content to engaged subscribers. Avoid sending to old, uncleaned lists, which can contain spam traps or inactive addresses. High bounce rates and spam complaints can quickly degrade your reputation and lead to Gmail marking your emails as dangerous, regardless of link security.
Regularly monitor your domain and IP address against major blocklists (or blacklists). While HTTPS helps secure data in transit, being listed on a blocklist can severely impact your deliverability and increase the likelihood of Gmail flagging your links as suspicious. Prompt removal from any blocklist is crucial. Staying off these lists requires diligent list management and adherence to email marketing best practices.
Finally, ensure your emails consistently pass SPF, DKIM, and DMARC authentication. These protocols are essential for proving to Gmail that your emails are legitimate and haven't been tampered with. Proper authentication is a fundamental layer of trust that can help avoid Gmail security warnings. Also, be cautious about using microdata markup if it's incorrectly implemented, as this can also lead to issues.
Best practices for linking in emails
Consistent domains: Ensure your sending domain and linked domains are consistent.
Valid SSL certificates: Verify SSL for all linked domains, including custom tracking domains.
Reputable ESPs: Choose an ESP with a strong reputation and dedicated IP options.
Clear link text: Ensure anchor text accurately reflects the destination URL, avoiding deception.
Monitor warnings: Regularly check Google Postmaster Tools for any security flags.
Final thoughts
While encountering a 'Suspicious Link' notification for an HTTPS website in Gmail can be frustrating, it's a testament to Google's rigorous efforts to protect its users. HTTPS is a crucial security measure, but it's only one piece of a much larger puzzle that Gmail considers when assessing link trustworthiness. Factors like sender reputation, link redirection practices, and overall domain health play an equally vital role.
Addressing these warnings requires a comprehensive approach focusing on technical configurations and consistent best practices in email marketing. By ensuring your authentication records are solid, your sender reputation is high, and your link tracking is properly secured, you can significantly reduce the chances of your legitimate HTTPS links being flagged. Continuous monitoring and swift action on any identified issues are key to maintaining strong email deliverability.
Views from the trenches
Best practices
Always ensure your custom tracking domains have valid, matching SSL certificates installed.
Regularly check your domain and IP reputation using Google Postmaster Tools.
Maintain a clean email list to reduce spam complaints and improve sender score.
Implement and monitor DMARC, SPF, and DKIM for robust email authentication.
Common pitfalls
Relying solely on HTTPS without addressing underlying sender reputation issues.
Using shared ESP IPs that have a history of spam or malicious activity.
Ignoring certificate mismatch errors on tracking subdomains, assuming HTTPS is sufficient.
Failing to update DNS records for custom tracking domains after ESP changes.
Expert tips
Check the actual CNAME records for your tracking domain to confirm they point correctly.
If using an ESP, verify their SSL handling for custom tracking links is robust.
Consider securing a dedicated IP if shared IP issues become a recurring problem for your sending.
Review your email content for any elements that might trigger phishing filters.
Marketer view
Marketer from Email Geeks says they've seen this issue before when a domain uses HSTS and the subdomain for click tracking doesn’t have a valid certificate.
2020-04-03 - Email Geeks
Marketer view
Marketer from Email Geeks says that a certificate error was observed when attempting to access a specific tracking subdomain, suggesting it as a potential cause.
Gmail displays a 'Suspicious Link' notification for a website you know uses HTTPS, especially when the link appears perfectly normal. We typically associate suspicious warnings with insecure HTTP sites or obvious phishing attempts, so seeing one for a legitimate, encrypted link is quite alarming. This often leads to questions about how 
Safe Browsing service, which identifies unsafe websites across the web. If the domain linked in your email has been flagged by Safe Browsing for malware, phishing, or unwanted software, 
Google Postmaster Tools. This invaluable resource provides insights into your sending reputation, spam rate, and authentication errors, which are all crucial indicators of how 
