What are the implications of disabling TLS 1.0/1.1 for outgoing email and what alternatives are available?

Key findings

• Fallback behavior: Disabling TLS 1.0/1.1 for outgoing email typically results in clear-text (unencrypted) transmissions to older recipient systems, not bounces. This is a crucial distinction, as email will still be delivered but without encryption.
• Current ecosystem: A vast majority of outbound email traffic today already uses TLS 1.2 or higher, indicating that older TLS versions constitute a very small percentage of current encrypted connections. For more on this, see what is TLS encrypted email traffic.
• Security vs. deliverability: While security best practices advocate for deprecating older, vulnerable protocols, doing so might lead to a philosophical debate on whether "broken encryption" is preferable to no encryption at all, especially if maintaining delivery is paramount.
• Advanced alternatives: Protocols like MTA-STS and DANE offer significantly enhanced transit security by mandating specific TLS versions and validating certificates, ensuring that email is only delivered over secure and authenticated connections.

Key considerations

• Recipient compatibility: Before disabling TLS 1.0/1.1, assess your recipient base. Although rare, some legacy systems might still rely on these older protocols, leading to unencrypted delivery or potential failure if opportunistic TLS is also dropped. Consider sporadic TLS encryption rates.
• Security posture: Disabling older TLS versions aligns with modern security practices and reduces exposure to known vulnerabilities. This is increasingly important as industry standards evolve, as noted by IETF RFC 8996, which deprecates TLS 1.0 and 1.1.
• Monitoring and reporting: Implement robust monitoring to track the percentage of emails delivered via clear-text or that fail due to TLS incompatibility after making changes. This data is crucial for assessing impact and informing clients, if you are an ESP.
• Client communication: For Email Service Providers (ESPs), transparent communication with clients about potential changes in encryption status and any resulting delivery behavior is essential to manage expectations.

Key opinions

• Deliverability first: Many marketers prioritize getting emails delivered, even if it means allowing fallback to clear-text for older, non-compliant systems rather than risking bounces from recipients.
• Opportunistic TLS importance: Opportunistic TLS is seen as a pragmatic approach, enabling encryption where supported while ensuring delivery otherwise. For further insights, see why is outbound TLS important for email marketing.
• Client impact: ESPs must consider whether their clients can tolerate potential increases in bounces or unencrypted transmissions before making strict TLS changes.
• Security vs. reality: While stricter TLS protocols like 1.2 and 1.3 are ideal, marketers must weigh the security benefits against the practicalities of a diverse and sometimes outdated internet infrastructure.

Key considerations

• Monitoring unencrypted volume: Marketers should actively monitor the volume of email sent unencrypted when using opportunistic TLS to understand their exposure.
• Risk tolerance: Assess the organization's or clients' tolerance for unencrypted mail versus the risk of non-delivery. This is a business decision balancing security and reach, as discussed by Sikich regarding TLS security.
• Client communication: For ESPs, clear communication with clients regarding TLS policies and their implications for deliverability and reporting is paramount. For more on this, see configuring SSL or TLS for email marketing.
• Gradual transition: Rather than an abrupt cut-off, a phased approach to deprecating older TLS versions might be more manageable, allowing time for recipients to upgrade their systems.

Key opinions

• Prioritize security: Older TLS versions are considered 'broken encryption' and should be phased out due to their inherent vulnerabilities.
• Clear-text is preferable to false security: Sending clear-text provides transparency, whereas using weak encryption can create a false sense of security.
• High TLS 1.2/1.3 adoption: Most email traffic already uses modern TLS versions, making the transition less impactful than some might anticipate. Refer to how TLS inbound affects email deliverability.
• Advanced security protocols: MTA-STS and DANE are recommended for significantly better transit security, enforcing validated TLS 1.2+ connections.

Key considerations

• Impact of strict enforcement: Requiring TLS 1.2+ can have a larger impact on deliverability than just honoring MTA-STS, potentially leading to more bounces if recipient servers are not updated. For context, see Microsoft's stance on disabling older TLS.
• MTA-STS/TLSRPT adoption: ESPs should consider implementing MTA-STS and TLSRPT, as the deliverability penalty for honoring these robust standards, even with some misconfigured policies, is found to be extremely low (e.g., a 0.00013% bounce increase).
• DNSSEC requirement for DANE: Implementing DANE requires DNSSEC, which might add a layer of complexity but significantly enhances security and trust in DNS records.
• Addressing certificate issues: Stricter TLS enforcement means issues like expired certificates will lead to non-delivery, emphasizing the need for proper certificate management. See what causes SSL/TLS key size errors.

Key findings

• Vulnerability to attacks: TLS 1.0 and 1.1 are susceptible to various attacks (e.g., BEAST, POODLE) due to weaknesses in their cryptographic primitives and design, making their continued use a security risk.
• Industry consensus: Major browsers, operating systems, and regulatory bodies (like PCI DSS) have deprecated or are planning to deprecate support for these older TLS versions, pushing for a move to TLS 1.2 and 1.3.
• Reduced attack surface: Eliminating older protocols reduces the complexity of security configurations and removes potential downgrade attack vectors, thereby strengthening the overall security posture.
• Mandatory upgrade: Regulatory compliance often mandates the use of strong encryption, effectively making the upgrade to TLS 1.2+ a requirement for many organizations. This contributes to better email deliverability.

Key considerations

• Compliance requirements: Organizations must ensure their email infrastructure complies with current security standards and regulations that increasingly deprecate older TLS versions. For example, CalCom Software advises disabling TLS 1.0.
• Interoperability: While most modern systems support TLS 1.2+, some niche or outdated systems might still rely on 1.0/1.1. A clear strategy for handling these exceptions, possibly through unencrypted fallback, is crucial.
• Long-term security: Investing in upgrades to TLS 1.2 and 1.3 is a long-term security measure that protects sensitive email communications from interception and tampering. Learn more about boosting email deliverability rates.
• Phased implementation: Documentation often recommends a phased approach to deprecation, allowing organizations to monitor impact and make adjustments, rather than an abrupt cutoff.