Summary
Transport Layer Security, or TLS, provides essential encryption for email in transit, securing communication between mail servers and preventing data interception. A sudden or significant drop in the percentage of TLS encrypted email traffic typically signals an issue with server configuration, either on the sending or receiving end. Common causes include outdated server software, misconfigured SSL/TLS certificates, a failure to properly advertise STARTTLS support, or the deprecation of older TLS versions. Additionally, network issues or incorrect DANE TLSA records can prevent secure connections. Since email TLS is often opportunistic, a failure in encryption typically means the email is still delivered, just in an unencrypted state.
Key findings
- TLS Definition and Purpose: Transport Layer Security (TLS) is a cryptographic protocol that encrypts email data as it travels between Mail Transfer Agents (MTAs) and receiving servers, ensuring privacy and integrity by preventing unauthorized interception and content sniffing during transit.
- Common Causes for Drops: A drop in TLS encrypted traffic percentages most often indicates misconfigurations on either the sending or receiving mail servers, outdated server software, or a failure to properly advertise STARTTLS support, causing connections to revert to unencrypted status.
- Sender and Recipient Side Faults: Issues can originate from the sender's Mail Transfer Agent (MTA) or the recipient's Mail Exchange (MX) server. This includes problems with SSL/TLS certificates, unsupported or outdated TLS versions, or an inability to complete the TLS handshake.
- Impact of Version Deprecation: The deprecation of older TLS versions, such as TLS 1.0 and 1.1, by providers can cause a drop in encryption if mail servers have not been updated to support newer versions, forcing unencrypted delivery.
- Network and DNS-Related Issues: Network problems, such as firewalls blocking ports or intermediaries interfering with the handshake, and misconfigured DANE TLSA records can also prevent TLS encryption, leading to unencrypted email delivery as a fallback.
Key considerations
- Check ESP and MTA Configuration: Regularly verify your Email Service Provider's and Mail Transfer Agent's configurations, ensuring proper SSL/TLS certificate setup, support for modern TLS versions, and correct advertisement of STARTTLS to prevent unencrypted fallbacks.
- Monitor Encryption Dashboards: Utilize encryption dashboards provided by your ESP or tools like Google Transparency Report to monitor inbound and outbound TLS percentages, which can help detect sudden drops indicating issues.
- Address Recipient Server Issues: Recognize that issues on the recipient's mail server, such as outdated software, misconfigured STARTTLS, or inability to support modern TLS versions, frequently cause a drop in encryption. While often outside your direct control, understanding this helps in diagnosis.
- Investigate Network Interferences: Be aware that network issues, including firewalls, proxies, load balancers, or routing problems, can interfere with the TLS handshake and lead to a drop in encrypted traffic.
- Understand Opportunistic TLS: Remember that TLS for email is typically opportunistic; if the secure connection fails to establish, mail will still be delivered unencrypted. This behavior explains why emails might still reach their destination despite a TLS drop.
What email marketers say
13 marketer opinions
Transport Layer Security, or TLS, is the foundational encryption layer for email, securing data as it moves between mail servers. A decrease in the percentage of TLS encrypted email traffic signals a critical issue, most commonly stemming from server-side problems at either the sender's Mail Transfer Agent or the recipient's Mail Exchange server. These issues frequently include misconfigurations, such as improper SSL/TLS certificate setups, outdated server software that fails to support modern TLS versions, or incorrect advertisement of STARTTLS, which initiates the secure connection. Network interferences, like firewalls blocking necessary ports or proxies, and misconfigured DANE TLSA records can also disrupt the secure handshake. Since TLS for email is typically opportunistic, a failure to establish an encrypted connection means the email is often still delivered, but in an unencrypted state, compromising privacy and security.
Key opinions
- TLS as Email Encryption Standard: Transport Layer Security, TLS, is the primary method for encrypting email traffic between Mail Transfer Agents (MTAs) and receiving MX servers, vital for safeguarding sensitive data in transit and maintaining privacy against content sniffing.
- Primary Causes of Percentage Drops: Drops in TLS encryption percentages are predominantly caused by misconfigurations on either the sending or receiving mail servers, including improper SSL/TLS certificate setup, outdated server software, or a failure to properly advertise STARTTLS support.
- Server-Side & Version Incompatibility: Issues frequently stem from a recipient server's inability or unwillingness to support modern TLS versions or complete the TLS handshake, often due to outdated software or configurations that force connections to fall back to unencrypted plain text.
- Network and DNS Related Factors: Network problems, such as firewalls blocking ports or intermediaries interfering with the TLS handshake, and incorrect or missing DANE TLSA records can also significantly contribute to a drop in encrypted email traffic.
- Impact on Sender Reputation and Security: TLS is crucial for email security and helps maintain a positive sender reputation by protecting user data. A drop indicates a potential security vulnerability, as messages are then sent unencrypted, making them susceptible to interception.
Key considerations
- Proactive Configuration Checks: Regularly verify your ESP and MTA settings, ensuring SSL/TLS certificates are properly configured, modern TLS versions are supported, and STARTTLS is correctly advertised to prevent fallback to unencrypted connections.
- Monitoring and Dashboards: Utilize encryption dashboards from your ESP or public resources like Google Transparency Report to actively monitor TLS percentages for both inbound and outbound traffic, helping to quickly identify and respond to any sudden drops.
- Addressing Recipient Server Issues: Understand that many TLS drop issues originate from the recipient's mail server, often due to outdated software, misconfigured STARTTLS, or an inability to support modern TLS versions, which may require coordinating with recipients or their providers if possible.
- Network Interference Investigation: Be prepared to investigate potential network issues, such as firewalls blocking necessary ports, network intermediaries like proxies or load balancers, or basic routing problems that can disrupt the TLS handshake.
- Understanding Opportunistic TLS: Remember that email TLS is typically opportunistic, meaning if the secure connection fails, the email will often still be delivered unencrypted. This highlights the importance of maintaining proper configurations to ensure security.
- DANE TLSA Record Management: Ensure DANE TLSA records are correctly configured and maintained in DNS, as misconfigurations or absence can lead to failed opportunistic TLS attempts and unencrypted email delivery.
Marketer view
Email marketer from Email Geeks explains TLS encrypted traffic is a method of encryption used for data in transit between ESP's MTAs and that a drop could indicate an error on the ESP's end or a fault at one of the sending MTAs.
30 Jul 2022 - Email Geeks
Marketer view
Email marketer from Email Geeks explains that TLS encrypts communication between sending MTAs and receiving MX servers, preventing content sniffing. He clarifies there's no direct relation between TLS and DMARC for encryption drop issues, and suggests checking with the ESP, as a drop might be due to different email streams or a temporary fault. He also specifies that TLS email encryption refers to MTA to MTA traffic and explains what an Encryption Dashboard shows, detailing inbound and outbound TLS percentages.
11 Oct 2024 - Email Geeks
What the experts say
3 expert opinions
TLS, or Transport Layer Security, is the standard method for encrypting email as it travels between servers, vital for securing communications. A decrease in its percentage indicates a break in this secure delivery, often due to server-side issues. These can include a recipient's Mail Transfer Agent, MTA, not supporting TLS, general server misconfigurations, or problems with SSL-TLS certificates. A common specific cause is the deprecation of older TLS versions by sending or receiving systems. Because TLS is often opportunistic, meaning encryption is attempted but not enforced, emails will still be delivered unencrypted if the secure connection fails, highlighting a security vulnerability.
Key opinions
- Core Function of TLS: Transport Layer Security, TLS, encrypts email traffic while it is in transit, ensuring secure communication between Mail Transfer Agents, MTAs, and preventing data interception.
- Impact of Older TLS Versions: The cessation of support for older TLS versions, such as TLS 1.0 and 1.1, by service providers can force mail servers to revert to unencrypted delivery, significantly impacting TLS percentages.
- Server-Side Configuration Issues: Drops in TLS percentages are frequently caused by recipient Mail Transfer Agents, MTAs, lacking TLS support, general server misconfigurations, or problems with SSL-TLS certificates, preventing secure handshakes.
- Opportunistic Nature and Fallback: TLS for email is typically opportunistic, meaning if a secure connection cannot be established, the email is still delivered unencrypted rather than failing entirely, posing a security risk.
- Indicators of Recovery: A sudden recovery in TLS percentages often suggests that an underlying issue, such as a misconfiguration or network problem, has been identified and resolved.
Key considerations
- Regularly Update Systems: Ensure your Mail Transfer Agents and Email Service Providers support current TLS versions and maintain proper server configurations to avoid falling back to unencrypted connections due to outdated technology.
- Monitor Delivery Metrics: Regularly check your email analytics and encryption dashboards for any unexpected drops in TLS delivery rates, as these can signal underlying server or network issues.
- Understand Opportunistic TLS: Be aware that email will often deliver unencrypted if TLS fails, emphasizing the critical need for proactive configuration checks to maintain data security, rather than relying on delivery as a sign of success.
- Investigate All Potential Causes: A drop in TLS can stem from various sources, including recipient server issues, certificate problems, and network interferences, requiring a comprehensive investigation to diagnose and resolve.
Expert view
Expert from Email Geeks suggests that a drop in TLS encrypted traffic could be due to older TLS versions (like v1.0 and v1.1) no longer being supported, causing MTAs to revert to unencrypted status. He notes that Constant Contact had announced end of support for these versions. He also implies that a sudden recovery indicates an issue was found and fixed.
19 Jul 2024 - Email Geeks
Expert view
Expert from Spam Resource explains that TLS, Transport Layer Security, encrypts email in transit. A drop in its percentage can occur if the recipient's Mail Transfer Agent, MTA, does not support TLS, due to server misconfiguration, or because of opportunistic TLS where encryption is not enforced.
6 Nov 2022 - Spam Resource
What the documentation says
5 technical articles
Transport Layer Security, TLS, is a vital cryptographic protocol that encrypts email traffic between mail servers, ensuring data privacy and integrity throughout its journey. The STARTTLS command often facilitates this by upgrading an existing plain text connection to a secure, encrypted session. A noticeable decline in the percentage of TLS-secured emails usually signals underlying configuration problems, such as a Mail Transfer Agent, MTA, that isn't properly set to enforce or prefer TLS connections. It can also occur if the MTA relies on outdated encryption standards or cipher suites that recipient servers no longer support, leading to failed secure handshakes and the delivery of unencrypted messages, which introduces security risks.
Key findings
- TLS for Email Security: Transport Layer Security, TLS, is a fundamental cryptographic protocol that encrypts email data during transit between mail servers, ensuring privacy and integrity by preventing unauthorized interception and tampering.
- STARTTLS Protocol Role: The STARTTLS command is crucial for opportunistic encryption, enabling mail servers to upgrade an existing plain text connection to a secure TLS session without requiring a separate communication port.
- MTA Configuration Impacts: A primary cause for a drop in TLS percentage is improper Mail Transfer Agent, MTA, configuration, including settings that do not enforce or prefer TLS, or the use of outdated cipher suites unsupported by recipient servers.
- Vulnerability from Drops: A decline in TLS encryption indicates potential security vulnerabilities, as it means emails are likely being transmitted unencrypted, exposing sensitive content to eavesdropping and man-in-the-middle attacks.
Key considerations
- Optimize MTA Configuration: Ensure your Mail Transfer Agent, MTA, is explicitly configured to enforce or prefer TLS for outgoing email and uses current, widely supported cipher suites to avoid failed negotiations.
- Leverage STARTTLS Properly: Confirm that your mail server correctly advertises and negotiates STARTTLS, as its proper function is essential for upgrading plain text connections to secure, encrypted sessions.
- Proactive Security Monitoring: Regularly monitor TLS encryption percentages for your email traffic, as a drop is a critical indicator of potential security vulnerabilities or misconfigurations that need immediate attention.
- Address Outdated Standards: Be aware that using outdated TLS versions or cryptographic protocols can lead to failed secure connections with recipient servers that no longer support them, resulting in unencrypted email delivery.
Technical article
Documentation from Google Workspace Admin Help explains that Transport Layer Security (TLS) ensures the privacy and integrity of emails by encrypting the data during transit between mail servers, preventing unauthorized interception and tampering.
8 Sep 2022 - Google Workspace Admin Help
Technical article
Documentation from Microsoft Learn details TLS as a cryptographic protocol used to establish a secure communication channel over the internet, essential for protecting email content from eavesdropping and data breaches as it travels between Exchange Online and other email servers.
29 Sep 2021 - Microsoft Learn
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