Summary
Using non-HTTPS links in emails carries significant negative consequences for email deliverability, sender reputation, and user experience. Mailbox providers, email clients, and web browsers increasingly flag or block emails with insecure links, often displaying prominent security warnings to recipients. This not only increases the likelihood of emails landing in spam folders but also erodes recipient trust and damages brand reputation. Insecure links can lead to reduced engagement, lower click-through and conversion rates, and even technical issues with tracking and rendering. Major email providers may disapprove of such practices, particularly for critical elements like list-unsub headers, and enterprise systems are especially sensitive to non-HTTPS traffic, further impeding message delivery.
Key findings
- Lower Deliverability & Sender Reputation: Emails with non-HTTPS links are more likely to be flagged by spam filters, blocked by security gateways, or land in the spam folder, directly contributing to a degraded sender reputation.
- Security Warnings & Reduced Trust: Email clients and web browsers prominently display security warnings for non-HTTPS links, which erodes recipient trust, damages brand reputation, and significantly increases the perceived phishing risk.
- Decreased Engagement & Conversions: Recipients are less likely to click on or engage with insecure links, leading to reduced click-through rates, lower conversions, and a poor overall user experience that can hinder campaign performance.
- RFC Violations & Provider Disapproval: Failing to use HTTPS for elements like 'list-unsub' headers violates RFC 8058, potentially leading to direct disapproval and deliverability issues with major email providers.
- Technical & Tracking Issues: Non-HTTPS tracking links can cause broken redirects or deliverability drops, and some email clients may interfere with the rendering or tracking of emails containing insecure content, leading to inaccurate performance data.
Key considerations
- Universal HTTPS Requirement: Ensuring all links, including tracking and landing pages, use HTTPS is crucial for maintaining security, trust, and optimal deliverability across all email campaigns.
- Impact on Critical Headers: The use of non-HTTPS for essential email headers, such as List-Unsubscribe, can lead to direct policy violations and disapproval from major mailbox providers, including Google, Microsoft, and Yahoo.
- Enterprise System Sensitivity: Corporate security gateways are highly sensitive to non-HTTPS traffic, often blocking or quarantining emails with insecure links, making it harder to reach recipients in enterprise environments.
- Cumulative Reputation Damage: Consistently using non-HTTPS links contributes to a cumulative degradation of sender reputation over time, making it increasingly difficult to achieve good inbox placement for all future campaigns.
- User Experience and Trust: Modern users expect secure connections; failing to provide HTTPS links significantly impacts user perception, leading to distrust, increased spam complaints, and potential abandonment of email content or linked resources.
What email marketers say
13 marketer opinions
Building on the previous summary's comprehensive overview, the consistent use of non-HTTPS links in emails creates a compounding series of negative effects that undermine an entire email program. These insecure links not only trigger immediate security warnings from browsers and email clients, causing recipients to lose trust and perceive phishing risks, but also directly degrade sender reputation over time. This leads to higher rates of messages being diverted to spam folders, diminished engagement, and ultimately, significantly lower conversion rates for campaigns. The technical fallout extends to broken tracking and rendering, and failure to use HTTPS for critical elements like unsubscribe headers can even lead to direct policy violations with major mailbox providers.
Key opinions
- Spam Filter & Blocking Risk: Emails containing non-HTTPS links are highly susceptible to being flagged by spam filters, blocked by security gateways, or diverted to spam folders, directly impairing deliverability.
- Recipient Distrust & Reputation Harm: Insecure links erode recipient trust, damage brand reputation, and elevate the perceived phishing risk, causing users to view the sender as unprofessional or potentially malicious.
- Reduced Engagement & Conversion: The presence of non-HTTPS links directly leads to lower click-through rates and decreased overall engagement, significantly impacting conversion goals due to recipient hesitation and security concerns.
- RFC Non-Compliance & Provider Penalties: Not using HTTPS for critical components like the List-Unsubscribe header violates RFC 8058, which can result in direct disapproval and deliverability penalties from major mailbox providers.
- Broken Analytics & Content Rendering: Non-HTTPS tracking links can malfunction, leading to broken redirects and inaccurate performance data, while some email clients may also interfere with the proper display of content.
- Challenges with Enterprise Systems: Enterprise-level email and security systems are often highly sensitive to non-HTTPS traffic, potentially leading to increased filtering or blocking of emails within corporate environments.
Key considerations
- Mandatory HTTPS Adoption: It is crucial to adopt HTTPS universally for all links within emails, encompassing tracking links, image URLs, and destination landing pages, to ensure security and prevent deliverability issues.
- RFC Compliance for Headers: Adhering to RFC 8058 by using HTTPS for the List-Unsubscribe header is essential to maintain compliance and avoid penalties or reduced deliverability from major mailbox providers.
- Proactive Link Auditing: Regular audits of email content for any non-HTTPS links are necessary to identify and remediate potential security vulnerabilities and protect sender reputation before campaigns launch.
- Recipient Trust and Behavior: Understand that insecure links directly erode recipient trust, increase the perceived phishing risk, and can lead to lower engagement and higher spam complaint rates.
- Enterprise Deliverability Barrier: The absence of HTTPS in links presents a significant barrier to delivery within enterprise environments, as corporate security systems are highly attuned to blocking or flagging insecure content.
Marketer view
Marketer from Email Geeks explains that not using HTTPS for list-unsub headers violates RFC 8058, can lead to disapproval from major email providers like Microsoft, Yahoo, and Google, and adds to the general 'grubbiness' of non-HTTPS body links. They also highlight that some enterprise systems may be sensitive to non-HTTPS traffic, impacting mail filtering and anti-malware, while generic consumer platforms are much less so.
23 Jul 2021 - Email Geeks
Marketer view
Marketer from Email Geeks suggests that Chrome might flag non-HTTPS links in emails, which would be a primary concern for user experience.
22 Jul 2021 - Email Geeks
What the experts say
3 expert opinions
Experts in email deliverability consistently highlight the critical impact of non-HTTPS links on sender reputation and email performance. While not always a direct cause of immediate blocking, the use of insecure connections significantly erodes recipient trust, triggering browser warnings and increasing the likelihood of user disengagement, spam complaints, and unsubscribes. Moreover, transmitting data over unencrypted HTTP poses a clear privacy risk, contributing to a diminished sender reputation that can become a pivotal factor in deliverability, especially for senders already experiencing other issues.
Key opinions
- Reputation & Tipping Point: Using non-HTTPS links lowers sender reputation and can be the critical factor that pushes a sender's deliverability over the edge when other issues are present.
- Observed Deliverability Impact: Deliverability experts have observed clear differences in how emails with HTTPS links are delivered compared to those with HTTP links.
- Recipient Trust Erosion: Modern web browsers prominently display 'Not Secure' warnings for HTTP pages, which significantly erodes recipient trust in the email and its sender.
- Increased User Complaints: Recipient discomfort with clicking insecure links can directly lead to higher rates of spam complaints or unsubscribes, negatively impacting list health.
- Privacy & Data Risk: Transmitting any data over an unencrypted HTTP connection poses a privacy risk, as information could be intercepted, further diminishing recipient confidence and brand perception.
Key considerations
- Mandatory HTTPS for Destinations: It is crucial to ensure that all landing pages and resources linked from emails use HTTPS to protect recipient trust and maintain deliverability.
- Impact on Sender Reputation: Recognize that using non-HTTPS links can subtly but significantly lower sender reputation, acting as a tipping point for deliverability issues if other problems exist.
- Recipient Trust and Action: Understand that 'Not Secure' warnings displayed by browsers for non-HTTPS pages directly erode recipient trust, potentially leading to increased spam complaints or unsubscribes.
- Mitigating Data Privacy Risks: Prioritize the use of HTTPS for all links to prevent the privacy risk of data interception over unencrypted HTTP connections.
- Observed Deliverability Variance: Be aware that email deliverability experts observe concrete differences in how emails are handled based on whether they contain HTTPS or HTTP links.
Expert view
Expert from Email Geeks explains that while non-SSL itself might not directly cause delivery problems, it lowers sender reputation and could be a tipping point if other problems exist and the sender is borderline.
15 Apr 2025 - Email Geeks
Expert view
Expert from Email Geeks states they definitively observe different delivery behavior for senders using HTTPS versus HTTP links.
2 Aug 2023 - Email Geeks
What the documentation says
5 technical articles
Emails containing non-HTTPS links face severe repercussions across the digital ecosystem, as major email clients and web browsers readily flag these connections with security warnings. This pervasive flagging not only alerts recipients to potential insecurity, significantly eroding their trust and deterring engagement, but also prompts suspicion from sophisticated security systems. Enterprise-level email filters, in particular, often identify non-HTTPS links as indicators of phishing or malware, leading to immediate blocking or quarantining of messages. Ultimately, the presence of insecure links can lead to messages being marked as spam or undelivered, directly undermining campaign effectiveness and damaging a sender's reputation for trustworthiness.
Key findings
- Widespread Security Warnings: Email clients, including Outlook, and all modern web browsers prominently display security warnings when non-HTTPS links are encountered or clicked, highlighting insecure connections to the recipient.
- Significant Trust Degradation: These pervasive warnings directly erode recipient trust in the sender and the message, increasing perceived phishing risks and concerns about insecure data transfer.
- Enterprise Blocking & Quarantining: Corporate security gateways and email filters are highly prone to blocking or quarantining emails containing non-HTTPS links, often associating them with phishing attempts or malware.
- Reduced User Interaction: The presence of security alerts and perceived risks significantly deters users from clicking non-HTTPS links, leading to decreased engagement and interaction with email content.
- Sender Reputation Impairment: Being linked to insecure connections causes recipients and automated systems to question the sender's legitimacy, harming overall sender reputation.
Key considerations
- Universal HTTPS Adoption: Ensure all links within emails, including tracking and destination URLs, utilize HTTPS to prevent security warnings and maintain recipient trust.
- Browser & Client Security Features: Recognize that email clients like Outlook and modern web browsers are designed to alert users about insecure connections, directly impacting email performance.
- Enterprise Deliverability Barriers: Be aware that corporate security systems are highly sensitive to non-HTTPS links, often leading to automatic blocking or quarantining of emails.
- User Trust & Click-Through Rates: Understand that displaying security warnings for insecure links directly diminishes user trust, severely reducing the likelihood of clicks and engagement.
- Avoiding Phishing Association: Refrain from using non-HTTPS links to avoid being flagged by security filters as potentially malicious or associated with phishing attempts.
Technical article
Documentation from Google Safety Center explains that using non-HTTPS (HTTP) links can trigger security warnings in browsers and email clients when clicked, signaling an insecure connection and potentially deterring users from interacting with the content, thereby reducing trust.
10 Feb 2025 - Google Safety Center
Technical article
Documentation from Microsoft Learn explains that email clients like Outlook often display security warnings for non-HTTPS links, which can lead recipients to distrust the email, mark it as spam, or prevent them from clicking due to perceived phishing risks or insecure data transfer.
20 May 2024 - Microsoft Learn
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