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 a legal requirement as well as good practice.

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): Uses AES-256 encryption on the sender’s device and keeps data 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 reduce risk in 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.
• Eligible Microsoft 365 and Office 365 users can use Microsoft Purview Message Encryption, depending on licence and tenant configuration.

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

Microsoft says Purview encrypted email can be read directly in supported Outlook clients, while other mail services receive opening instructions.

Its recipient experience, revocation options, and suitability for customer communications depend on licence, tenant configuration, policy setup, and the recipient's email client.

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

The Radicati Group estimates that around 392.5 billion emails will be sent and received worldwide each day in 2026.

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 maintaining customer trust.

FAQs

What Does Email Encryption Protect?

It protects message content by making it unreadable to anyone without the right access or key.

Who Needs Email Encryption?

Any organisation sending personal, financial, legal, medical, or confidential business information by email may need it.

Why Add Authentication as Well as Encryption?

Encryption protects content, while authentication helps confirm the intended person is the one opening it.

References

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

Data Security Incident Trends, Information Commissioner's Office

Email Statistics Report, 2024-2028 - Executive Summary, The Radicati Group, 2024

How Many Work Emails Is Too Many?, The Guardian, 2019

UK Consumer Report: Email Security, Beyond Encryption, 2024

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

Send S/MIME or Microsoft Purview Encrypted Emails in Outlook, Microsoft Support, 2026

Message Encryption FAQ, Microsoft Learn, 2026

Reviewed by

Sabrina McClune, 18.06.24

Sam Kendall, 02.06.26

This content is for general information only and is not legal advice.