What Is TLS Encryption And How Does It Affect Email Delivery?

Imagine sending a private client proposal or financial update by email without knowing that anyone along the way could read or even change it. That is what can happen when emails are not encrypted. They travel like postcards that anyone handling them can see. TLS encryption is like an invisible shield that protects your emails and is important for email delivery.

It encrypts your messages as they move between servers. This ultimately helps in keeping your private information safe from spying or tampering. However, TLS does more than protect privacy. It also helps your emails get delivered. It affects your messages delivery by inbox providers.

Here we will explain what TLS is and how using TLS correctly improves both your email security and delivery success.

TLS (Transport Layer Security) is a technology that keeps data safe when it moves across the internet. When used for email, TLS encrypts your messages as they travel between mail servers. So, no one can read or change them without permission.

TLS came after an older system called SSL (Secure Sockets Layer). SSL was created in the 1990s to help protect internet data but is now outdated and less secure. TLS versions 1.2 and 1.3 are newer and stronger, using better methods to keep data safe and making it much harder for anyone to intercept your information.

To put it simply:

• SSL is the old and weaker way to protect data (now mostly replaced).
• TLS is the modern and stronger version of SSL which keeps your data secure.
• HTTPS websites use TLS or SSL to protect your browsing.

TLS operates with the mail sending system known as the SMTP in email. When both the sender and receiver support TLS servers, the email is encrypted completely as it is transferred. However, when TLS is not utilized in one of the servers, the email may not be encrypted. The email lacks protection and in some cases, reduced the chances of the email making it to the inbox safely.

Overall, using TLS encryption helps to keep your emails private and improves the chances they get delivered properly.

TLS helps keep emails safe and makes sure they get delivered properly by doing three important things:

TLS encrypts your email in a way that if somebody attempts to snoop on your email during transmission, they would not be able to read it. This is particularly significant when it comes to companies such as banks, health care and e-commerce that deal with sensitive information on a daily basis.

TLS checks that the email has not been altered while it is traveling. In case a person attempts to alter the message, the system will immediately detect it. This safeguards firms against email fraud.

TLS involves the use of special digital certificates by trusted authorities in order to prove that the email comes from the actual sender. This prevents impersonators and assures the email providers about your messages.

Together, these three things make email communication safer and help build a good reputation for your business. A strong reputation means your emails are more likely to reach the inbox instead of getting blocked or sent to spam.

The link between using TLS and getting your emails into inboxes is stronger than many people think. Email providers like Gmail, Yahoo, and Outlook look at both your email content and your technical setup before deciding to send your messages to users. Using TLS is one of the clearest signs that you can be trusted.

Big email providers prefer senders who always use TLS. When your domain makes sure emails are sent securely, it shows you care about privacy and technical reliability. This helps improve your sender reputation, making it more likely your emails will reach inboxes.

In fact, over 95% of emails sent to Gmail in 2024 were protected by TLS which shows its effect on email delivery. Email providers are starting to block or lower the priority of emails that are not encrypted, especially marketing emails, because they see them as less safe or lower quality.

If your TLS security is not working right - like having expired certificates or handshake failures - your emails might bounce more or get blocked. Domains with expired TLS certificates can have higher bounce rates than those with valid encryption.

Some dangers are not easy to see. A hacker tricks one of the servers into turning off TLS in a downgrade attack. This makes the email travel without encryption, a technique called STARTTLS stripping. When that happens, the hacker can intercept or change the email while it is being sent. This is known as a man-in-the-middle (MITM) attack.

Sending emails without TLS encryption is not just a security problem. It also makes email providers think your system might be old or hacked. This can lower your chances of getting your emails delivered. When encryption is not consistent, it is a red flag that you might not have full control over your email setup.

Domain owners can use two tools to protect against these email risks: MTA-STS and TLS-RPT.

• MTA-STS makes sure emails are only accepted if they are sent over a secure and encrypted connection. This stops hackers from forcing emails to be sent without TLS encryption.
• TLS-RPT sends reports when something goes wrong with email encryption, allowing administrators to quickly find and fix the issue.

Using both tools helps to keep your emails safe. This makes sure they get delivered properly by catching hidden encryption problems before they cause trouble.

STARTTLS is great, but it has a weakness: if an attacker can trick the receiving server into thinking TLS isn’t available, the email gets sent in plain text. This is called a downgrade attack, and it’s why basic TLS alone isn’t enough for high-security email.

That’s where MTA-STS and DANE come in. They’re two standards that enforce TLS encryption — making sure emails are only delivered if the connection is secure.

What Is MTA-STS?

MTA-STS (SMTP MTA Strict Transport Security) is a standard that tells sending servers: “You must use TLS to deliver email to this domain. If you can’t establish a secure connection, don’t deliver the email at all.”

It works by publishing a policy file on your website that says:

• Which mail servers support TLS
• What certificates they should present
• How long the policy is valid for

Sending servers cache this policy and refuse to deliver email over unencrypted connections.

MTA-STS vs STARTTLS: What’s the Difference?

What Is DANE?

DANE (DNS-based Authentication of Named Entities) takes a different approach. Instead of relying on certificate authorities (like HTTPS does), DANE uses DNSSEC to publish certificate information directly in DNS.

With DANE, the receiving domain publishes a TLSA record in DNS that contains a fingerprint of its TLS certificate. Sending servers check this record and only connect if the certificate matches.

DANE requires DNSSEC — if your domain doesn’t have DNSSEC enabled, you can’t use DANE.

MTA-STS vs DANE: Which Should You Use?

The short answer: use MTA-STS if you can, and add DANE if you have DNSSEC.

Here’s a quick comparison:

Basic MTA-STS Setup Steps

Setting up MTA-STS involves three main pieces:

1. Create the MTA-STS policy file

• Hosted at https://mta-sts.yourdomain.com/.well-known/mta-sts.txt
• Lists your MX servers and policy mode
• Example policy:
• version: STSv1
• mode: enforce
• mx: mx1.aurorasendcloud.com
• mx: mx2.aurorasendcloud.com
• max_age: 86400

2. Publish the STS DNS record

• A TXT record at _mta-sts.yourdomain.com
• Contains the policy version ID so senders know when it changes

3. Set up TLS-RPT reporting

• A DNS record that tells senders where to send TLS failure reports
• Similar to DMARC’s RUA reports, but for TLS issues
• Example: _smtp._tls.yourdomain.com TXT "v=TLSRPTv1; rua=mailto:tls-reports@yourdomain.com"

Do You Need MTA-STS Right Now?

For most businesses, standard TLS + DMARC is enough to get started. MTA-STS is an advanced layer that makes sense if:

• You work in finance, healthcare, or government
• You handle highly sensitive data
• You want the strongest possible email security
• You already have SPF, DKIM, and DMARC at p=reject

Think of it this way: SPF, DKIM, and DMARC are your front door lock. MTA-STS and DANE are the security system and deadbolt. You don’t need the deadbolt until you’ve already got the basic lock working.

At Aurora SendCloud, we support MTA-STS and can help you set it up when you’re ready. Our team handles the technical details so you can focus on sending great emails that get delivered.

If you use Aurora SendCloud for sending emails, setting up TLS is easy. There is no complicated server work needed. Aurora SendCloud handles encryption smoothly and gives you clear visibility of all your outgoing emails.

You can turn TLS on or off for each receiving domain. This way, emails go securely where possible, and fallback options are used when needed.

Aurora SendCloud gives you live logs and reports about any TLS errors. So, your team can fix problems before they affect delivery.

Aurora SendCloud keeps up with the latest TLS security standards. So, you don't have to worry about manual updates.

Marketers and developers can feel confident that every email campaign is sent safely, improving both security and delivery success.

Using TLS to keep email secure and trustworthy helps your email messages get through and retains credibility with your audience.

Using TLS encryption is not just about protecting your data. It is also about gaining the trust and ensuring that your emails do reach inboxes of individuals. Encrypted email connections assist in establishing positive reputation for your sender address. Conversely, non-encrypted emails or those that are configured improperly will be blocked, bounced away or ignored, adding to missed opportunities.