Why is outbound TLS important for email marketing?

Key findings

• Security: TLS encrypts email traffic during transit, protecting message content from eavesdropping and tampering. This is akin to using HTTPS for website browsing, ensuring that sensitive information (like login details or personal data) remains private.
• Deliverability: While not always a direct factor for immediate blocklisting, the absence of TLS can negatively impact sender reputation over time. Major mailbox providers (MBPs) increasingly favor senders who utilize secure connections, and some may display warnings to recipients if emails arrive unencrypted.
• Compliance: Regulations like GDPR mandate that organizations enforce security measures for personal data as much as reasonably feasible. Not enabling outbound TLS for emails containing personal data could be considered a failure to meet these obligations.
• Recipient trust: Warnings about unencrypted messages, particularly from providers like Gmail, can erode recipient trust and decrease engagement with your email campaigns.
• Universal application: The benefits and requirements of outbound TLS apply across all email sending structures, irrespective of whether your primary sending is through Google, Microsoft, or another provider.

Key considerations

• Mandatory implementation: Most experts and marketers agree that TLS should no longer be an optional setting for email, as secure communication is now a baseline expectation. For more on this, read our article on configuring SSL/TLS on sending domains.
• Broader security implications: Ensure all external resources linked within your emails, such as call-to-action (CTA) URLs, images, and CSS, also utilize HTTPS. This holistic approach to security enhances overall message integrity and sender trustworthiness.
• Monitoring TLS rates: Senders should monitor their TLS encryption rates to ensure consistent security and identify any potential issues that could lead to unencrypted delivery. Drops in TLS rates can indicate underlying network or configuration problems. Learn what causes a drop in TLS encrypted email traffic.
• Enhancing email security: Prioritize email encryption as a fundamental aspect of your email marketing strategy. Elastic Email suggests that encryption adds a layer of email security by making content inaccessible to intercepting hackers, reinforcing user privacy.

Key opinions

• No longer optional: Many marketers believe that outbound TLS should be a standard, non-optional setting, reflecting an industry shift towards universal email encryption.
• Gmail warnings: A significant concern for marketers is Gmail's practice of displaying warnings for messages that lack TLS encryption, which can alarm recipients and reduce open rates.
• Holistic security: Marketers are increasingly aware that securing email extends beyond the message itself to include all linked resources (e.g., images, CTAs), which should also use HTTPS for consistency and trust.
• Brand legitimacy: Using TLS/SSL connections can enhance a sender's perceived legitimacy with mail services and recipients, contributing to a positive brand image.

Key considerations

• Impact on recipient engagement: Warnings about unencrypted email can deter recipients from opening or interacting with messages, directly affecting marketing campaign performance. Securing your links and images with HTTPS also plays a role in sender reputation, as explained in our guide on why HTTPS is important for email marketing.
• Universal applicability: TLS requirements are not limited to specific platforms like Gmail or Google Workspace. They are a universal standard that applies to all email sending structures and receiving mail servers globally, underscoring the need for widespread adoption.
• Security beyond the email: All web resources linked or embedded in emails, such as images, CSS, and call-to-action (CTA) URLs, must also be served over HTTPS to maintain a consistent security posture. This helps prevent mixed content warnings and reinforces trust. Learn more about why your emails might be failing to be delivered.
• Impact on marketing: Mailgun advises using TLS encryption to strengthen data security over the web and in email marketing campaigns, emphasizing its dual role in security and marketing effectiveness.

Key opinions

• Reputation factor: While TLS may not have an immediate, direct impact on deliverability, it's considered one of many data points used by reputation and anti-threat systems to assess sender trustworthiness.
• Legal compliance: Experts warn that not enabling outbound TLS could constitute a failure to enforce security as required by regulations like GDPR, especially when handling personal data.
• Data privacy: TLS is crucial for encrypting email traffic in transit, preventing sensitive information (e.g., bank statements, login details, password resets) from being exposed in plain text to interceptors.
• Industry standard: Outbound TLS is effectively the email equivalent of HTTPS for websites; it's a widely accepted standard for secure online communication.
• Universal application: The requirement for TLS applies universally across all email sending and receiving environments, regardless of the specific email provider or infrastructure used.

Key considerations

• Enhancing sender reputation: Implementing TLS contributes positively to your sender reputation by signaling a commitment to security, which mail providers consider. This complements other authentication measures like SPF, DKIM, and DMARC. Learn about the simple guide to DMARC, SPF, and DKIM.
• Legal and ethical imperative: Beyond technical benefits, TLS is increasingly viewed as an ethical and legal obligation for businesses handling user data, particularly in regions with strong privacy laws.
• Protection of sensitive data: For transactional emails containing sensitive information, TLS is indispensable. Even for marketing emails, it protects user privacy during the journey, upholding brand integrity.
• Adherence to recommendations: Experts recommend consulting authoritative guides, like those from M3AAWG, for best practices in TLS deployment. For example, the M3AAWG Initial Recommendations for Email TLS Deployment are highly relevant. Consider how these technical solutions improve your overall deliverability, as detailed in our guide on technical solutions from top performing senders.

Key findings

• Core function: TLS encrypts the entire email session from the sending mail server to the receiving mail server, ensuring the confidentiality and integrity of the message content during transmission.
• Data protection: It prevents 'man-in-the-middle' attacks and eavesdropping, where malicious actors might intercept and read email content if it were transmitted in plain text via SMTP.
• Privacy mandate: Standards and recommendations from bodies like M3AAWG (Messaging, Malware and Mobile Anti-Abuse Working Group) strongly advocate for TLS as a critical component of email privacy and security efforts.
• Protocol evolution: TLS has evolved to become the successor to SSL, providing stronger cryptographic security for data in transit, and is now the accepted standard.

Key considerations

• Mandatory adoption: While opportunistic TLS is common (where encryption is used if available), there's a growing push for enforced TLS to ensure all email is encrypted. This is often achieved through mechanisms like DANE (DNS-based Authentication of Named Entities).
• Protecting message content: LuxSci states that TLS protects the transmission of email message contents by encrypting them during transit, making it inaccessible to unauthorized parties. This is its primary security benefit for email.
• Data integrity: Beyond encryption, TLS also provides data integrity, meaning it can detect if any part of the message has been altered during transit. This is critical for transactional emails where accuracy is paramount.
• Universal requirement: The principles of secure email delivery using TLS apply globally, irrespective of the sending or receiving email provider, emphasizing its role as a fundamental internet standard. Understanding this is key to broader email domain authentication best practices.