What are the risks of including email addresses as URL parameters?

Key findings

• Data leakage: Email addresses embedded in URLs are often stored in server logs, analytics tools, browser histories, and can be exposed through referrer headers or shared links. This significantly increases the risk of PII exposure.
• Compliance violations: Using PII in plain text URL parameters can violate terms of service for analytics platforms, like Google Analytics, and potentially breach data privacy regulations (e.g., GDPR, CCPA).
• Security vulnerabilities: This practice introduces information exposure vulnerabilities, making it easier for malicious actors to harvest email addresses for spam, phishing, or other fraudulent activities.
• SEO and deliverability impact: While less direct, poor URL parameter management can lead to SEO issues like duplicate content. Although not a primary deliverability factor, any practice that increases security risks can indirectly impact sender reputation or lead to blocklisting if the exposed data is misused to send spam, potentially causing emails to go to the junk folder. Learn more about what happens when your domain is on an email blacklist.

Key considerations

• Alternative identifiers: Implement non-reversible hashes (e.g., MD5) or UUIDs instead of raw email addresses for unique user identification in URLs. This allows for one-click functionality without direct PII exposure.
• Secure transmission: Always use HTTPS for any URL containing sensitive data, even if hashed. This encrypts the data in transit, though it doesn't prevent its storage in logs once processed.
• Privacy policy alignment: Ensure your data handling practices, especially with URLs, align with your company's privacy policy and relevant data protection laws. Negligence in this area can lead to severe reputational and legal consequences.
• URL encoding: If any data must be passed in a URL, ensure it is properly URL-encoded to prevent misinterpretation and potential vulnerabilities. Improper encoding can affect email deliverability and spam filtering.

Key opinions

• Convenience driver: The primary motivation is often to streamline user workflows, like enabling immediate access to events without requiring a separate sign-up page.
• Lack of awareness: Many marketers are not fully aware of the technical ramifications and potential data leaks associated with putting PII in URL parameters until they are alerted by security professionals or experience issues.
• Post-discovery concern: Once informed of the risks, marketers quickly realize the necessity of finding alternative, more secure methods to achieve similar functionality.
• Historical precedent: There are anecdotal accounts from marketers recalling past incidents where email addresses leaked into public search results due to improper URL handling.

Key considerations

• User experience vs. security: Marketers should prioritize data security over marginal gains in user convenience, especially when secure alternatives exist.
• Stakeholder education: It's crucial for marketing teams to be educated on the security implications of their practices and involve technical teams in solution design.
• Impact on sender reputation: Practices that compromise user data or privacy can negatively affect sender reputation, increasing the likelihood of emails landing in spam folders. This can happen indirectly if exposed emails lead to abuse complaints.
• Privacy regulations: Ignoring data privacy in URL parameters can lead to significant penalties under regulations like GDPR, something marketers should be acutely aware of when considering data collection and usage practices.
• Seeking alternatives:Marketers frequently inquire about safer ways to pass user data, suggesting a growing awareness and desire for best practices.

Key opinions

• High security risk: Experts consistently label this practice as a major security concern, capable of exposing sensitive PII to various third parties and malicious actors.
• Negligence and compliance: Such methods are often seen as negligent regarding a company's terms of service and privacy policy, potentially leading to legal repercussions and reputational damage.
• OWASP guidance: Cybersecurity frameworks like OWASP (Open Web Application Security Project) explicitly detail the risks of information exposure through query strings, underscoring the severity of the vulnerability.
• Real-world data leaks: Experts recall instances of major companies inadvertently leaking millions of user emails due to this practice, serving as a stark warning.
• Impact on deliverability: While direct causal links to spam filtering might be debated, any practice that increases security risks or leads to data misuse can indirectly harm sender reputation and result in emails going to spam.

Key considerations

• Prioritize security by design: Integrate data protection and security considerations from the outset of any system or campaign design, rather than as an afterthought.
• Use hashed or encrypted identifiers: Employ cryptographic hashing (like MD5 or SHA256) or encryption for any PII transmitted via URLs, ensuring the original data is not exposed.
• Educate internal teams: Ensure all personnel, especially those involved in marketing and IT, understand the risks and proper handling of sensitive data in URLs. This includes understanding how tracking links affect deliverability.
• Implement server-side solutions: For advanced personalization, leverage server-side sessions or lookups based on secure, non-identifying tokens rather than client-side URL parameters.

Key findings

• Information exposure: Technical documentation, such as the OWASP guide on information exposure, explicitly lists the risks of sensitive data appearing in query strings.
• Log data retention: Email addresses included in URLs can persist indefinitely in server logs, proxy logs, and analytics databases, even after the initial interaction.
• Browser history and referrers: URLs containing PII are stored in browser histories and can be transmitted via referrer headers to other websites, creating multiple points of leakage.
• SEO impact: URL parameters, while useful for tracking, can inadvertently create duplicate content issues and inefficient crawl budgets for search engines, complicating SEO efforts as outlined by various guides on URL parameter handling for SEO.

Key considerations

• Use HTTPS exclusively: All web communications involving sensitive data should be over HTTPS to encrypt the data during transit. This is a fundamental security requirement.
• Avoid PII in query strings: Best practices dictate that sensitive information should never be passed directly in URL query strings. Secure alternatives like POST requests or server-side sessions should be used.
• Proper URL encoding: Any characters that are not part of the standard URL set must be percent-encoded to ensure correct interpretation and to prevent potential vulnerabilities. This also has implications for how URL length affects email deliverability.
• Redirect management: When redirects are used, ensure that sensitive URL parameters are not inadvertently carried over to subsequent pages or external sites. Consider the deliverability drawbacks of using redirects.