What Is Email Encryption? Explainer & Statistics

Email encryption disguises email content to protect it from being intercepted. It’s a key element of outbound email security.

Encryption is often paired with identity authentication in secure email solutions to ensure that only the intended recipient can read the contents.

What Is Email Encryption?

Email encryption is a security technique that involves encoding the contents of an email message.

Encryption scrambles the message so that it becomes unreadable without the correct decryption key.

The decryption key can be held permanently or accessed by proving your identity through recipient authentication.

There are various encryption algorithms available, offering different levels of strength depending on the sensitivity of the data.

Who Needs to Encrypt Their Emails?

Anyone transmitting sensitive information via email should use encryption.

This is essential to prevent data breaches, identity theft, and cyber attacks.

Encryption is particularly important for businesses and professionals that handle high volumes of personal or confidential data.

In many sectors, encrypting customer data in digital transmission is not just good practice but a legal requirement.

Explore how to send secure business emails.

Why Is Email Not Secure?

Email has existed for as long as the internet, but it was never designed with security in mind.

When you send an email, it travels through multiple nodes in a network.

At any one of these points, a bad actor could intercept the data - whether at your mail server, your recipient’s, or anywhere in between.

If your email contents are not encrypted, they can be read or even manipulated during transmission.

See what a cyber criminal could do with your data.

What Data Needs Encrypting?

Sensitive information such as personally identifiable information or confidential documents should always be encrypted.

This includes names, addresses, and birthdays, along with passwords, banking details, business contracts, and proprietary data.

The risk is not limited to external communications. Internal emails within an organisation or across the same network are also vulnerable.

Failing to encrypt sensitive data can lead to data breaches, regulatory penalties, and long-term reputation damage.

Learn more about personally identifiable information.

How Does Email Encryption Work?

Email encryption converts readable content into a secure format that cannot be understood without access to a decryption key.

1. Encryption Process: When you send an encrypted email, the content is scrambled using a cryptographic algorithm. This converts the text into ciphertext - a jumbled, unreadable format.
2. Types of Encryption: The point at which encryption occurs, and its strength, depends on the method used. For example:
   • TLS (Transport Layer Security): Encrypts emails during server-to-server transmission. If a secure connection cannot be established, the email may be sent unencrypted.
   • S/MIME (Secure/Multipurpose Internet Mail Extensions): Provides end-to-end encryption using a pair of cryptographic keys and requires a digital certificate for both sender and recipient.
   • AES-256 (Advanced Encryption Standard): Offers military-grade encryption, encrypting data on the sender’s device and keeping it secure until the recipient decrypts it.
3. Decryption Process: When the email arrives, the recipient’s credentials or key unlocks the original content.

This means that even if a message is intercepted, only the intended recipient can read it.

Encryption Best Practices

How can you make sure the right emails are encrypted? Here are some email encryption best practices to follow.

Matching Your Setup to Your Needs

Email encryption can be implemented manually, message by message, or automatically based on certain rules or triggers.

If you’re delivering sensitive documents at scale, automated encryption may be required.

Make sure your method of initiating encryption matches how and where you handle sensitive information.

Choose the Right Encryption Solution

Outlook users can encrypt messages natively, but this may not be suitable for all types of sensitive data.

Specialist tools such as Mailock offer enhanced security and user-friendly features for customer communications.

For outbound messages to clients or customers, choose a tool that meets both your needs and theirs.

Compare the best secure email services for business.

Adding Authentication to the Mix

Encryption alone isn’t enough to prevent the most common cause of data breaches: human error.

By adding recipient authentication, you can ensure only the intended person can access the message - even if it’s sent to the wrong address.

Combining encryption with authentication helps eliminate risk from your outbound communications.

Learn how recipient authentication works.

Email Encryption in Outlook/365, Gmail, & iOS

Most email clients, including Outlook, Gmail, and iOS Mail, offer basic encryption features:

• Most providers use TLS encryption by default and offer optional S/MIME with a digital certificate.
• Microsoft 365 enterprise users (with an E3 licence or above) gain access to Microsoft 365 Message Encryption (MPME).

The key difference between S/MIME and MPME is compatibility. S/MIME requires the recipient’s client to support the same encryption standard.

MPME works across most platforms, offering protection regardless of the recipient's email provider.

"The rights management (MPME) feature is intended as a tool to prevent accidental misuse and is not a security boundary."

Microsoft spokesperson, 2022

MPME’s encryption strength is designed to prevent errors rather than provide high security.

It also has limitations on volume, making it unsuitable for customer communications at scale.

For enterprise-grade protection, a dedicated secure email service is recommended.

Learn more about secure email services for business.

What Native Email Encryption Doesn’t Do

Built-in encryption options are not designed to handle large-scale customer communications.

Volume, functionality, and security all present challenges - but user experience is key, too.

For example, are you sending documents that customers need to complete and return?

Standard encryption such as S/MIME secures content on delivery only. It doesn’t support secure two-way communication.

Businesses are responsible for ensuring both sides of the email exchange are protected.

Specialist secure email services make it easy for recipients to reply securely with the same level of encryption and protection.

Explore secure email solution features.

Key Statistics

The latest email encryption statistics from trusted sources highlight why secure email matters.

Misfires

Emails sent to the wrong person are the top cause of reported data breaches in the UK, according to the Information Commissioner's Office (ICO).

Interception

A 2017 study from the University of Michigan and University of California found that between 4% and 10% of internet traffic is intercepted in transit.

Volume

According to Statista, an estimated 361.6 billion emails are sent and received every day in 2024.

Conversations

The average office worker sends 40 emails and receives 121 emails each day, according to research cited by The Guardian.

Error

More than one in four UK adults has accidentally shared personal data with the wrong recipient by email, according to our 2024 research.

Reputation

46% of businesses that experience a data breach suffer damage to their reputation and brand value, according to CSO Online.

Vital for Digital Security

Email encryption is a vital component of digital security, transforming sensitive information so it can’t be accessed by unauthorised users.

With options like TLS, S/MIME, and AES-256, you can choose the right level of protection for your needs.

Combine encryption with authentication to prevent leaks caused by human error.

While basic encryption tools are widely available, specialist secure email solutions are essential for enterprise and regulatory compliance.

Implementing the right encryption strategy is key to safeguarding communications and building trust in a digital world.

References

The Security Impact of HTTPS Interception, University of Michigan and University of California, 2017

Daily Number of Emails Worldwide, Statista, 2024

UK Consumer Report: Email Security, Beyond Encryption, 2024

Does a Data Breach Really Affect Your Firm’s Reputation?, CSO Online, 2024

Reviewed by

Sabrina McClune, 18.06.24

Sam Kendall, 17.06.25