TLS Email Encryption, Explained

When it comes to transmitting sensitive information, email security is a priority, whether you’re a business or a consumer.

TLS email encryption has become a vital part of keeping data safe in transit, shielding it against potential interception.

Let’s explore how TLS email encryption works, what it offers, and how you can set it up.

Contents:

• Understanding TLS
• How Does TLS Work?
• Benefits of TLS-Encrypted Email
• Limitations of TLS
• Is TLS Encryption Secure?
• Alternative Email Encryption
• TLS: A Summary

Understanding TLS

TLS stands for Transport Layer Security.

It’s a protocol that protects data as it travels between systems, such as websites or email servers.

TLS replaced the older SSL (Secure Sockets Layer).

It helps stop unauthorised parties from reading data as it moves across networks.

When you use TLS for email, you add two important security layers.

• Encryption: This scrambles the connection between servers, making sure the data stays hidden during transit.
• Authentication: This confirms a server’s identity before building a secure connection, so data is only sent to a genuine server.

How Does TLS Work?

TLS sets up a protected connection between email servers, keeping messages safe as they travel.

The encryption process has a few steps:

1. When you send an email via TLS, the sender’s server tries to start a secure connection with the receiving server. It performs a TLS ‘handshake’ where servers exchange digital certificates to check each other’s identities.
2. Once they’re verified, they agree on encryption standards. TLS uses symmetric encryption, where both servers share a secret key, to protect the connection.
3. The sending server transmits the email’s content through the encrypted link. Anyone who intercepts the data would see only unreadable information.

Benefits of TLS-Encrypted Email

TLS is good for stopping unauthorised access to emails while they move from one server to another.

It doesn’t offer end-to-end encryption (covering messages throughout their journey), but it helps solve a few email security problems.

Protection from Eavesdropping and Men-in-the-Middle

Man-in-the-middle attacks are a global threat.

These attacks happen when a malicious actor intercepts and potentially alters the communication between two parties without their knowledge.

TLS makes emails unreadable during transmission.

Increased Data Privacy for Everyday Emails

TLS adds a layer of security to regular email exchanges, helping guard information that’s not highly sensitive but still private.

If you must meet data regulations, like those from the ICO or GDPR, TLS can help you stay compliant.

You might need stronger encryption to fully protect very sensitive data.

Preventing Data Leakage

TLS lowers the chance of data leaks between email servers by protecting information in transit.

Devices and systems at either end may still be weak spots, but TLS covers the path between them.

Simplified Deployment

TLS is mostly handled by the email server, so users rarely need to do anything.

It scales well and suits consumers and businesses of all sizes.

Limitations of TLS

TLS has many plus points, but there are limits.

Server-To-Server Protection Only

TLS protects emails in motion between servers.

But it’s not true end-to-end encryption.

Once the email reaches the recipient’s server, it’s no longer encrypted.

Dependency on the Recipient’s Server

If the recipient’s server doesn’t support TLS, a message may be sent in plain text (depending on the email provider).

For this reason, many use other encryption methods in combination with TLS to ensure protection throughout message transfers.

"TLS encryption is an effective measure for securing data during transmission, but it does not address vulnerabilities at either end of the communication."

– Mike Wakefield, CTO, Beyond Encryption

Implementing TLS in Your Organisation

TLS is often easier to set up than some end-to-end encryption methods because it works at the server level.

Here’s a quick guide:

Make Sure TLS Compatibility Is in Place

Most email services, such as Microsoft 365, Gmail, and Exchange, support TLS natively.

But check that both your and the recipient’s servers have TLS enabled.

Switch on TLS on Your Email Server

Configuring your server for TLS is important.

Usually, you can easily configure the settings to require TLS for inbound and outbound mail.

Create Policies and Standards

Set a policy that requires TLS for all emails containing sensitive information.

Explain what to do if TLS isn’t available.

Audit and Monitor Regularly

Check your email server logs to make sure TLS is running smoothly.

Look for any unencrypted emails to review and address errors.

Is TLS Encryption Secure Enough for Business Email?

TLS encryption protects emails between servers, but your needs may go further – especially if you are in a regulated sector.

If your company deals with highly sensitive data, such as financial or medical records, TLS alone might not do the job:

• It only protects the email between servers.
• Once it arrives in the recipient’s inbox, it’s decrypted.

If the recipient’s server is compromised, the data could be at risk.

Consider stricter rules in industries like healthcare, finance, or law.

TLS helps with compliance, but many regulations suggest end-to-end encryption and other safeguards.

"For everyday communication, TLS alone may provide a reasonable level of security.

However, organisations should assess whether it’s sufficient for sensitive data or compliance requirements."

– Paul Holland, Founder, Beyond Encryption

Alternative Email Encryption Methods

TLS is useful, but other methods might be better for certain needs.

Let’s take a quick look.

S/MIME (Secure/Multipurpose Internet Mail Extensions)

S/MIME is a trusted encryption standard with digital signature support.

It encrypts the email’s content at the message level, so it stays protected even after it reaches the inbox.

Digital signatures confirm the sender’s identity and show if anyone has tampered with the message.

Pros:

• S/MIME encrypts the content itself, giving strong protection post-delivery.
• Digital signatures let recipients verify who sent the email and check the message’s integrity.
• Certificates from trusted authorities help manage trust and authenticity.

Cons:

• Certificates need to be issued, renewed, and revoked, which can be time consuming.
• S/MIME depends on Certificate Authorities (CAs), which brings in third-party reliance.
• Some email clients need extra configuration to fully support S/MIME.

PGP (Pretty Good Privacy)

PGP also offers encryption and digital signatures, but it uses a decentralised ‘web of trust’ instead of central certificate authorities.

Users create and manage their own keys, then build trust directly with others.

Pros:

• Users generate their own key pairs, giving more control.
• PGP is well known and used in personal and professional contexts.
• It doesn’t require certificates, which reduces outside dependence and costs.

Cons:

• PGP can be hard for non-technical users to set up correctly.
• Managing a web of trust is tough in large organisations.
• Many email clients don’t support PGP natively, so extra software may be needed.

End-to-End Encryption (E2EE)

E2EE makes sure only the sender and the recipient can see the email’s contents.

It encrypts messages on the sender’s device and only decrypts them on the recipient’s device.

This means the message stays secure throughout its journey.

Pros:

• The message is encrypted from when it’s sent until it’s opened by the recipient.
• Servers can’t read the content, since encryption happens at the user level.
• Even if messages are intercepted during transmission, they remain unreadable.

E2EE is a top choice for sensitive data, like financial or medical records.

Tools like our own secure email solution, Mailock, add features such as recipient verification, which keeps data extra safe.

TLS: A Summary

TLS is a widely supported way to secure email data while it’s in transit.

It offers good protection from interception, eavesdropping, and data theft.

It can help organisations meet basic security requirements, and it may support some compliance needs.

However, TLS isn’t end-to-end, and it relies on the recipient’s server supporting TLS.

Companies that handle highly sensitive data might consider S/MIME, PGP, or an E2EE secure email solution like Mailock.

FAQs

Is TLS Widely Supported by Email Providers?

Most modern email providers support TLS by default, including Gmail and Outlook.

If the other person’s server doesn’t support TLS, your message might end up unencrypted.

How Can I Set Up TLS?

You can switch on TLS by installing a valid digital certificate and requiring TLS for inbound and outbound mail.

Many hosting providers have built-in tools for this.

How Can I Check If My Emails Use TLS?

Look in your email headers for a note on TLS.

Some clients show a padlock icon when TLS is active.

What Are TLS’s Downsides?

TLS encrypts mail between servers only.

It doesn’t protect data once it’s on the recipient’s server.

If that server doesn’t support TLS, your email goes in plain text.

How Does TLS Differ from End-to-End Encryption?

TLS secures the path between servers.

End-to-end encryption covers the entire journey from your device to the recipient’s, so nobody else can read it.

References

How To Prevent Man-In-The-Middle Attacks, Cybernews, 2025

Google Transparency Report, Google, 2025

Reviewed by

Sam Kendall, 23.01.2025

Sabrina McClune, 23.01.2025