Does opportunistic TLS impact email deliverability negatively?

While not a direct cause of emails landing in spam, consistently low opportunistic TLS rates can signal underlying issues to mailbox providers. High rates contribute to a better sender reputation and are preferred by receivers.

How can I check my current TLS encryption rates?

You can monitor your TLS encryption rates through tools like Google Postmaster Tools, which provide insights into traffic and encryption metrics for your sending domains.

Is it better to use mandatory TLS instead of opportunistic TLS?

Mandatory TLS ensures all emails are encrypted or fail to deliver, offering higher security. However, it can lead to higher bounce rates if recipient servers don't support TLS. Opportunistic TLS prioritizes delivery, making it common for bulk senders.

What specific configurations can improve my opportunistic TLS rates?

Ensure your sending servers support and prioritize modern TLS versions (1.2 or 1.3), use strong cipher suites, and resolve any SSL/TLS key size errors or network issues that might prevent successful handshakes.

Are there penalties from mailbox providers for low TLS encryption?

Major mailbox providers generally don't directly penalize for opportunistic TLS fallback. However, Google's new bulk sender guidelines emphasize TLS, suggesting that consistently low encryption could impact reputation over time.

Are sporadic TLS encryption rates common for bulk email senders using opportunistic TLS? - Technical - Email deliverability - Knowledge base

For bulk email senders, optimizing deliverability means navigating a complex landscape of technical configurations and mailbox provider requirements. One area that often prompts questions is Transport Layer Security (TLS) encryption rates, particularly when relying on opportunistic TLS.

The core question many ask is whether sporadic or inconsistent TLS encryption rates are a common occurrence when sending high volumes of email with opportunistic TLS, and what this means for overall email deliverability. This is a crucial point, as secure transit of email is becoming increasingly important for sender reputation.

Understanding opportunistic TLS in email

Opportunistic TLS allows mail servers to try to establish an encrypted connection using Transport Layer Security (TLS). If the connection fails, or the receiving server doesn't support TLS, the email is still sent, but over an unencrypted plain text connection. This differs from "forced TLS," which would fail the delivery if encryption isn't possible, prioritizing security over guaranteed delivery.

This approach is widely adopted because it prioritizes delivery over mandatory encryption, ensuring emails reach their destination even if a secure channel cannot be established. Many major email providers, including services like

Microsoft Exchange Online, use opportunistic TLS by default, attempting to encrypt connections whenever possible. This broad adoption underscores its role as a foundational security layer for email in transit, as detailed on Wikipedia's page about Opportunistic TLS.

While it provides a significant improvement over completely unencrypted email, the "opportunistic" nature means that a 100% encryption rate cannot always be guaranteed for every single message. This inherent flexibility is what leads to the discussions around sporadic encryption rates for bulk email senders.

Factors contributing to sporadic TLS rates

The primary reason for observing sporadic (or less than 100%) TLS encryption rates lies in the very design of opportunistic TLS. It relies on both the sending and receiving mail servers successfully negotiating a TLS handshake. If any part of this negotiation fails, or if an intermediate server doesn't support TLS, the connection will default to unencrypted.

Several factors can contribute to these fluctuations. Issues with network intermediaries, such as firewalls or proxies, can interfere with TLS handshakes between servers. Even temporary server load or brief network glitches on either the sender's or recipient's side can prevent a successful TLS negotiation, leading to a temporary drop in encrypted traffic.

Understanding why there might be a drop in TLS percentage requires examining the entire email path. Sporadic encryption could also stem from issues like SSL/TLS key size errors or general server misconfigurations, which can disrupt the secure connection establishment.

Sending server	Receiving server	Outcome
Yes	Yes	TLS encrypted
Yes	No	Sent unencrypted
No	Yes	Sent unencrypted
No	No	Sent unencrypted

Impact on deliverability and sender reputation

For bulk email senders, a natural concern is whether sporadic TLS encryption rates negatively affect email deliverability or sender reputation. Generally, for opportunistic TLS, a less than 100% rate does not directly cause emails to be blocked or sent to spam. Mailbox providers like

Gmail and

Yahoo, prioritize delivery and will still accept messages over unencrypted connections if TLS isn't viable.

However, the landscape is shifting. Major providers are increasingly emphasizing email security. Google, for example, has highlighted the importance of TLS in its bulk sender guidelines. While they may not directly penalize for every unencrypted send, a consistently low TLS rate might be seen as a sign of suboptimal sending practices, potentially influencing sender reputation over time.

Demonstrating a commitment to email security, including high TLS rates, contributes positively to your overall email deliverability. It's important to consider how TLS matters for inbox placement and why outbound TLS is important for building and maintaining trust with mailbox providers.

Aim for consistent TLS

Proactive monitoring: Regularly monitor your TLS encryption rates, especially using tools like Google Postmaster Tools.
Infrastructure checks: Ensure your mail transfer agents (MTAs) and network are correctly configured to prioritize and facilitate TLS.
Stay updated: Keep your email sending software and systems updated to support the latest TLS versions.

Strategies for optimizing opportunistic TLS rates

Even with the inherent variability of opportunistic TLS, bulk email senders can implement strategies to optimize their encryption rates. The goal is to ensure your sending infrastructure is consistently prepared to attempt and successfully negotiate TLS whenever possible, minimizing fallback to unencrypted connections.

First, ensure your own mail servers are robustly configured and regularly updated to support the latest, most secure TLS versions. Outdated TLS protocols or weak cipher suites can lead to failed handshakes and unencrypted delivery. Proactive management of your server's SSL or TLS configurations is fundamental.

Second, continuous monitoring of your TLS performance using analytics, such as those from Google Postmaster Tools, is crucial. This helps identify trends and pinpoint specific recipient domains or networks where TLS failures are more common. Armed with this data, you can investigate and address underlying issues, like why TLS errors occur when sending to Gmail.

Suboptimal configuration

Outdated TLS versions: Using TLS 1.0/1.1 or older, which are increasingly deprecated.
Weak cipher suites: Employing less secure encryption algorithms.
Network restrictions: Firewalls or proxy servers blocking or degrading TLS connections.
Lack of monitoring: No visibility into actual TLS encryption rates or connection errors.

Optimized configuration

Modern TLS support: Prioritizing TLS 1.2 or 1.3 for all outbound connections.
Strong cipher suites: Configuring the server to use only robust, secure cryptographic ciphers.
Network optimization: Ensuring network paths are clear and conducive to TLS handshakes.
Proactive monitoring: Utilizing tools to track and alert on drops in TLS encryption.

Views from the trenches

Best practices

Actively monitor TLS rates in Google Postmaster Tools for trends and specific recipient issues.

Ensure your MTAs are correctly configured to prioritize and support modern TLS versions.

Conduct regular audits of your email infrastructure to prevent misconfigurations that impact TLS.

Common pitfalls

Assuming 100% opportunistic TLS, as network factors can always cause variability.

Ignoring sporadic drops in TLS rates, which could indicate underlying network or configuration problems.

Failing to update server software, leading to compatibility issues with newer TLS requirements.

Expert tips

Focus on the stability of your own sending infrastructure rather than external network factors.

Engage with your ESP to understand their TLS practices and any observed anomalies.

Investigate specific recipient domains if consistently lower TLS rates are observed.

Expert view

Expert from Email Geeks says a lot of ESPs struggle with sporadic opportunistic TLS, but it's not "everyone." Focusing on your own infrastructure's ability to initiate TLS can help, as some issues might be localized to specific senders' setups rather than a universal problem.

2019-02-20 - Email Geeks

Marketer view

Marketer from Email Geeks says they haven't observed sporadic TLS encryption rates over 120 days using SalesForce Marketing Cloud (SFMC), though they acknowledged a need to check if their setup was mandatory or opportunistic.

2019-02-20 - Email Geeks

Enhancing email security through consistent TLS

While sporadic TLS encryption rates can indeed be observed for bulk email senders utilizing opportunistic TLS, they are not necessarily a universal constant for "everyone." The degree of variability depends heavily on the robustness of your sending infrastructure, the configurations of receiving mail servers, and the intricacies of intermediate network paths.

Rather than being a direct deliverability blocker, consistently low TLS rates can indicate underlying technical issues or a lack of optimal security posture. Prioritizing the latest TLS versions, ensuring proper server configuration, and continuous monitoring are key steps in maximizing your encrypted email traffic. This proactive approach helps build trust with mailbox providers.

Ultimately, achieving the highest possible TLS encryption rates for your outgoing email reflects a commitment to security, which is increasingly valued by major mailbox providers. This contributes positively to your overall email ecosystem, fostering better deliverability and sender confidence in the long run.