Does TLS directly prevent emails from going to spam?

While not a primary factor, TLS enhances sender trustworthiness and is increasingly a baseline expectation for reputable senders.

What is opportunistic TLS?

Opportunistic TLS is when the sending server attempts encryption but will still deliver the email in plain text if the receiving server doesn't support TLS.

Why should I disable older TLS versions?

Older TLS versions, such as 1.0 and 1.1, have known security vulnerabilities. Disabling them ensures stronger encryption and better security.

How does TLS relate to sender reputation?

TLS contributes to a positive sender reputation by demonstrating a commitment to security and privacy, building trust with mailbox providers.

Do I need an SSL certificate for email TLS?

Yes, an SSL/TLS certificate is required to enable TLS encryption for your email communication between servers.

Does using TLS matter for email deliverability or inbox placement? - Technical - Email deliverability - Knowledge base

When we send emails, we expect them to arrive securely. Transport Layer Security (TLS), previously known as SSL, is the standard encryption protocol that ensures privacy between sending and receiving mail servers. A common question arises, especially with visual cues like padlock icons in email clients: does TLS encryption directly impact email deliverability or inbox placement?

The short answer is nuanced. While TLS is fundamental for secure communication, its absence doesn't always lead to immediate inbox filtering. However, its importance for sender reputation and overall email ecosystem health is undeniable, and overlooking it can have subtle, yet significant, long-term consequences for your email program.

The role of TLS in email security

TLS encrypts the communication channel during email transit, protecting content from eavesdropping. When an email server connects to another, it attempts to establish a TLS-encrypted session. This process is crucial for preventing unauthorized access to sensitive information as emails traverse the internet.

Most email systems use what is called opportunistic TLS. This means the sending server attempts to establish a TLS connection, but if the receiving server doesn't support it, the email will still be delivered unencrypted. For email senders, ensuring your mail transfer agent (MTA) is configured to use opportunistic TLS by default is a basic security measure. Some senders also implement more stringent protocols like MTA-STS or DANE to enforce TLS, ensuring mail is either encrypted or not delivered at all.

The padlock or similar icon that appears in some email clients, like Gmail, indicates that the email was received via a TLS-encrypted connection. While this offers reassurance to recipients, it's important to remember that this icon reflects the transport encryption, not necessarily end-to-end encryption of the message content itself.

Implementing TLS is therefore a critical step for maintaining the privacy and integrity of your email communications. It builds a foundation of trust with receiving mail servers and helps avoid situations where your emails might be exposed to interception. Considering how essential it is, every sender should configure TLS on their domains for email marketing.

TLS and its direct impact on deliverability

Does using TLS directly affect whether your email lands in the inbox or the spam folder? Historically, mailbox providers have not heavily penalized emails simply for lacking TLS encryption. The primary focus of deliverability filters remains on content, sender reputation, and authentication protocols like SPF, DKIM, and DMARC. You can learn more in our guide to DMARC, SPF, and DKIM.

However, this doesn't mean TLS is irrelevant. While it may not directly trigger a spam block, it's becoming an increasingly expected practice. Not using TLS, or using outdated versions, can be seen as a sign of a less reputable sender, contributing negatively to your overall sender score over time. It can also lead to warnings, such as the 'red lock' icon in Gmail, which can alarm recipients.

The importance of TLS for secure delivery is highlighted by leading mailbox providers. For instance, Google's transparency report shows that a vast majority of emails delivered to Gmail are encrypted via TLS. While not strictly mandatory for deliverability (in some cases), it is increasingly a standard expectation. Being an outlier in this regard could lead to subtle reputation degradation, and may make it more likely your domain ends up on an email blacklist (or blocklist).

Consider the contrast between direct impact and indirect influence:

Minimal immediate impact

Filtering: Emails typically not blocked solely for lack of TLS.
Inbox placement: Less direct influence compared to sender reputation factors.

Crucial for trust

Trust signals: Builds confidence with mailbox providers.
Sender score: Contributes to overall domain reputation.
User perception: Prevents security warnings in recipient inboxes.

The indirect benefits and future importance of TLS

Beyond opportunistic encryption, the version of TLS you employ also matters. Older protocols like TLSv1.0 and TLSv1.1, and especially SSLv2 and SSLv3, are considered insecure and have been deprecated by the Internet Engineering Task Force (IETF). Continuing to use them might offer a false sense of security, as they are vulnerable to various attacks.

Modern email ecosystems expect at least TLSv1.2, with TLSv1.3 becoming more prevalent. If your system cannot negotiate a secure connection using these modern versions, it indicates a security vulnerability. It's crucial to disable support for deprecated TLS versions on your mail servers to improve your outbound TLS for email marketing.

Here's an example of how you might configure a Postfix mail server to enforce modern TLS versions, rejecting older, insecure ones. This ensures your outbound connections prioritize robust encryption, falling back to plaintext only if modern TLS is genuinely unsupported.

Example Postfix TLS Configurationnone

smtp_tls_security_level = may
smtp_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
smtp_tls_protocols = TLSv1.2, TLSv1.3

The trend is clear: security standards are tightening. Organizations like CISA emphasize the importance of secure email transport. While their directives might currently focus on the mere presence of STARTTLS, such as in Binding Operational Directive 18-01, the implicit push is towards stronger, modern encryption. Failing to keep up with these evolving standards could eventually lead to deliverability issues, even if it's not an explicit blocklist or blacklist criterion today.

Always prioritize modern TLS

Best practice: Configure your mail servers to use TLSv1.2 or TLSv1.3. This aligns with industry best practices and strengthens your email security posture.
Security: Protects your email content from interception and builds trust with receiving servers and recipients.
Future-proofing: Prepares your sending infrastructure for stricter requirements from major mailbox providers, like new Outlook sender requirements.

Views from the trenches

Best practices

Ensure your mail transfer agent (MTA) is configured to use opportunistic TLS by default, as it's a basic security measure.

Implement modern TLS versions (1.2 and 1.3) and disable older, insecure protocols like TLSv1.0, TLSv1.1, SSLv2, and SSLv3.

Prioritize securing your email channels, as this contributes to overall sender reputation and compliance with evolving industry standards.

Common pitfalls

Believing that opportunistic TLS alone guarantees full email security; it only encrypts if the receiving server supports it.

Overlooking the deprecation of older TLS versions, which can create a false sense of security and expose vulnerabilities.

Failing to maintain up-to-date email sending infrastructure, potentially leading to deliverability challenges as standards tighten.

Expert tips

Consider protocols like MTA-STS and DANE for enforced TLS, ensuring email is either encrypted or not delivered.

Remember that the visible padlock icon in email clients signifies transport encryption, not end-to-end content encryption.

Align your email security practices with broader internet security trends, as mailbox providers increasingly weigh security in reputation assessments.

Expert view

Expert from Email Geeks says: While it might not heavily affect delivery, using TLS is considered table stakes for bulk email senders, akin to basic infrastructure requirements.

2023-05-11 - Email Geeks

Expert view

Expert from Email Geeks says: TLS isn't strictly a deliverability issue unless you're specifically sending over IPv6, in which case it becomes absolutely necessary.

2023-05-11 - Email Geeks

Ensuring secure email delivery

While the direct impact of TLS encryption on email deliverability and inbox placement might not be as pronounced as factors like sender reputation, content relevance, or authentication protocols, its foundational role in email security is indisputable. Ignoring TLS can lead to a degraded sender image and potential issues as industry standards evolve. It's an essential part of an effective email program.

Ultimately, prioritizing secure email transmission with modern TLS versions not only safeguards your communications but also strengthens your overall sender confidence. It’s a proactive step that aligns your sending practices with the best interests of both recipients and mailbox providers, contributing to long-term deliverability success and helping you avoid landing on a common blocklist (or blacklist).