What are the implications of disabling TLS 1.0/1.1 for outgoing email and what alternatives are available?
Michael Ko
Co-founder & CEO, Suped
Published 7 Jun 2025
Updated 16 Aug 2025
9 min read
The digital landscape is constantly evolving, and with it, the standards for secure communication. Transport Layer Security (TLS) is at the forefront of this evolution, serving as the backbone for encrypting internet traffic, including email. Older versions, specifically TLS 1.0 and 1.1, have long been identified as having security vulnerabilities. This has led many organizations and internet service providers to advocate for, and implement, their deprecation.
The move to disable these older protocols for outgoing email raises important questions. Will it lead to increased email bounces? How will it affect deliverability? What alternatives are available to maintain, or even enhance, email security without disrupting communication flow? These are crucial considerations for anyone managing email infrastructure.
Understanding the implications of this shift and proactively adopting modern encryption standards is essential not just for security, but also for ensuring reliable email delivery and maintaining a strong sender reputation. I'll delve into the current landscape, the potential challenges, and the robust solutions available for securing your outgoing email.
The necessity of deprecating older TLS protocols
TLS 1.0 and 1.1, first introduced in 1999 and 2006 respectively, have served their purpose but are now considered outdated due to known security weaknesses. These include vulnerabilities to downgrade attacks, where attackers force a connection to use a weaker, older protocol version, and a lack of support for modern, stronger cryptographic algorithms. Industry consensus, including recommendations from the National Cyber Security Centre, emphasizes the transition to more robust protocols.
Major technology companies and organizations have already deprecated or announced plans to deprecate support for these older TLS versions. For example, Microsoft 365 services deprecated TLS 1.0 and 1.1 years ago. Similarly, Google's updated bulk sender guidelines require TLS 1.2 or higher for receiving email. This widespread shift signals that relying on older TLS versions for email communication is becoming increasingly insecure and unreliable, potentially affecting your email deliverability.
For email, the primary concern is the potential for unencrypted transmissions, or clear-text fallback. Unlike web browsing, where an insecure connection often results in a browser warning or blocked access, email systems frequently attempt to deliver mail unencrypted if a secure connection cannot be established. This means your sensitive email content could be transmitted over the internet without any encryption, making it vulnerable to interception.
Implications of disabling TLS 1.0/1.1 for outgoing email
When considering disabling TLS 1.0 and 1.1 for outgoing email, the immediate concern for many is whether this will result in a significant number of bounced emails. While some older mail servers might not support TLS 1.2 or 1.3, the more common outcome is a fallback to an unencrypted connection, rather than an outright bounce. This is due to the opportunistic nature of email TLS, where encryption is attempted but not strictly enforced by default.
The vast majority of modern email systems already support TLS 1.2 or higher. According to recent surveys, over 97% of outbound email traffic already uses TLS 1.2. This means the percentage of mail that would fall back to clear-text (unencrypted) or bounce due to a lack of support for current TLS versions is relatively small, but still present. The decision then becomes a balance between ensuring maximum security and reaching every possible recipient.
For senders, particularly bulk emailers or those dealing with sensitive information, this fallback to unencrypted communication can be problematic. It can erode trust, expose data, and potentially impact your overall email deliverability and inbox placement if recipient servers prioritize secure connections. The goal should be to minimize unencrypted transmissions as much as possible.
The impact of disabling old TLS for email
Disabling TLS 1.0/1.1 for outgoing email primarily means that your mail server will no longer attempt to negotiate a connection using these outdated protocols. If the recipient mail server also does not support TLS 1.2 or 1.3, the email will either fallback to an unencrypted connection (if opportunistic TLS is used), or it will bounce. While bounces are generally reported, clear-text transmissions might go unnoticed without specific monitoring.
Modern encryption standards and their benefits
The industry standard for email encryption has moved definitively towards TLS 1.2 and, increasingly, TLS 1.3. These newer versions offer significant cryptographic improvements, better performance, and enhanced resistance to attacks compared to their predecessors. Adopting these modern standards is not just about compliance, but about genuinely securing your email communications and protecting sensitive data.
For email senders, embracing TLS 1.2 or 1.3 means that your messages are encrypted with the strongest available algorithms during transit. This reduces the risk of eavesdropping and tampering. It also signals to receiving mail servers that you adhere to current security best practices, which can positively influence your domain reputation and ultimately improve overall email deliverability.
While most email service providers (ESPs) and major mailbox providers like Google and AWS have mandated or strongly recommend TLS 1.2+, there might still be niche or legacy systems that do not. Monitoring your email logs and deliverability reports will provide insights into the percentage of your outgoing mail that is currently encrypted and highlight any domains that might be problematic due to outdated TLS support. This awareness is key to making informed decisions about your TLS configuration.
Introduced stronger ciphers and hashing algorithms
Currently widely supported, recommended minimum
TLS 1.3
Faster, more secure, removes outdated features
Latest standard, increasing adoption
Implementing advanced security measures: MTA-STS and DANE
Beyond simply enforcing TLS 1.2 or 1.3, there are advanced protocols that offer even stricter security for email in transit. Mail Transfer Agent Strict Transport Security (MTA-STS) and DNS-based Authentication of Named Entities (DANE) are two such alternatives that enforce encrypted connections and prevent downgrade attacks.
MTA-STS allows email senders to declare that their mail servers only accept secure connections. It works by publishing a policy via HTTPS, which receiving servers can then check. If a mail server attempts to deliver email to a domain with an MTA-STS policy, it will verify the certificate and enforce TLS encryption. This prevents attackers from forcing unencrypted connections or delivering mail to unauthorized servers. Implementing MTA-STS can significantly bolster your outbound email security.
DANE, on the other hand, ties TLS certificate validation to DNS records, secured by DNSSEC. This provides an even stronger layer of security by allowing mail servers to verify the authenticity of a recipient's TLS certificate directly through DNS. While DANE requires DNSSEC to be enabled on your domain, it offers a robust defense against man-in-the-middle attacks and certificate impersonation. Both MTA-STS and DANE move beyond opportunistic TLS to mandatory, validated encryption, significantly reducing the risk of clear-text transmissions.
Example MTA-STS DNS TXT recordDNS
_mta-sts.yourdomain.com IN TXT "v=STSv1; id=20230308T100000Z;"
While adopting these strict protocols might lead to a minimal increase in bounces due to improperly configured recipient servers, the security benefits often outweigh the risks. Organizations, especially Email Service Providers (ESPs) handling large volumes of mail, must weigh the trade-offs between widespread deliverability and stringent security. Many have found that the percentage of impacted mail is negligible, given the broad adoption of modern TLS versions globally. This is crucial for maintaining secure email traffic.
Opportunistic TLS
Flexibility: Attempts encryption but falls back to clear-text if secure connection fails, ensuring delivery.
Wider reach: Delivers to virtually all mail servers, including older or misconfigured ones.
Security concern: Allows unencrypted transmission, posing a security risk for sensitive data.
Enhanced security: Protects against downgrade and man-in-the-middle attacks.
Potential bounces: May result in bounces for recipients on non-compliant or misconfigured systems.
Best practices for a smooth transition
Disabling older TLS versions and moving to stricter protocols like TLS 1.2, 1.3, MTA-STS, and DANE is a strategic decision that requires careful planning. Start by analyzing your current email traffic to understand the percentage of mail still relying on TLS 1.0/1.1 or falling back to clear-text. This data will help you assess the potential impact on your recipient base. Tools that offer email deliverability testing can provide valuable insights.
It is also vital to communicate any upcoming changes to your clients or internal stakeholders, especially if you are an ESP. Inform them about the security benefits and the minimal, yet possible, impact on deliverability to certain legacy systems. Providing clear bounce reports and guidance on how to address them can help manage expectations and build trust.
Finally, continuous monitoring of your email delivery, particularly TLS encryption rates, is paramount. Be prepared to address any unexpected increases in bounces or unencrypted deliveries. While the transition to modern TLS versions is largely smooth, proactive management ensures that your email remains both secure and reliably delivered, avoiding issues like landing on a blocklist or blacklist.
Views from the trenches
Best practices
Actively monitor your email traffic to identify the percentage of emails still using older TLS versions or falling back to clear text.
Prioritize implementing MTA-STS for domains sending sensitive information to enforce strict TLS connections and prevent downgrade attacks.
Educate clients or internal teams about the security benefits of deprecating older TLS versions and how it might affect a small portion of legacy systems.
Common pitfalls
Assuming that disabling older TLS versions will automatically lead to email bounces; often, it results in unencrypted transmission.
Neglecting to monitor your TLS encryption rates after making configuration changes, leading to undetected clear-text fallback.
Underestimating the philosophical question of whether sending unencrypted email is preferable to not sending it at all.
Expert tips
Leverage DMARC reports to gain visibility into your email authentication and encryption statistics, helping you understand TLS usage.
If you're an ESP, strike a balance between offering robust security and ensuring deliverability for a diverse client base, possibly by offering tiered security options.
For domains where deliverability is absolutely paramount, consider a phased approach to tightening TLS requirements, starting with monitoring.
Expert view
Expert from Email Geeks says that based on recent surveys, the vast majority of outgoing email traffic already uses TLS 1.2, with most of the remainder being clear-text transmissions due to older systems.
2022-08-16 - Email Geeks
Marketer view
Marketer from Email Geeks says they initially believed disabling older TLS versions would result in bounces, but realized it would likely fall back to no encryption instead.
2022-08-16 - Email Geeks
Embracing a secure email future
The deprecation of TLS 1.0 and 1.1 for outgoing email is a necessary step towards a more secure internet. While it may introduce minor challenges with legacy systems, the overwhelming majority of email traffic already utilizes modern TLS versions like 1.2 and 1.3, mitigating the risk of widespread disruption. The primary concern shifts from outright bounces to the unintended fallback to unencrypted transmissions for a small percentage of mail.
By understanding these implications and proactively adopting advanced security protocols like MTA-STS and DANE, organizations can ensure their outgoing email remains both secure and reliably delivered. Continuous monitoring and transparent communication with stakeholders are key to navigating this transition smoothly, safeguarding your data, and enhancing your email deliverability rates.
