Types of Email Encryption

Have you ever wondered how secure your emails really are?

Cybercriminals are getting more advanced every year, making email encryption increasingly important for protecting email information.

As someone who's helped companies to protect their communications for years, I’ve seen the devastating impact a lack of proper security can have.

From data breaches to financial losses, the consequences can be serious.

Fortunately, understanding the different types of encryption can empower you to safeguard your communications.

In this guide, I’ll walk you through the most effective encryption methods, from widely adopted standards like TLS to the highly secure AES-256.

Along the way, I’ll share practical insights from working in the field, helping you to make the best decisions about protecting your emails from threats.

Contents:

• Why Email Encryption Matters
• Main Types of Email Encryption
• Additional Types of Encryption
• Understanding Email Encryption

Why Email Encryption Matters

Email encryption is crucial for keeping sensitive information private and secure.

With cyber threats constantly evolving, simply sending a 'normal' email is no longer safe.

It could be intercepted or manipulated at many points in its journey.

By using the right types of encryption, you can make sure that even if your email is intercepted, the contents are unreadable to anyone without the right decryption key.

Unfortunately, not all types of email encryption are alike.

For example, TLS (Transport Layer Security) is used by a lot of email providers to secure data in transit, but it only encrypts content between email servers, leaving messages unprotected in inboxes.

To protect data from sender to receiver (called end-to-end email encryption), it's important to know the difference between the different types.

Types of Encryption for Email Security

Email encryption can be split into two main categories: transport-level encryption and end-to-end encryption.

Each type serves a specific purpose in protecting your emails, and understanding these differences is key to choosing the right security.

1. Transport-Level Encryption: SSL and TLS

SSL (Secure Sockets Layer)

SSL was introduced in 1995 as one of the first protocols to secure email content through authentication and encryption.

Cyber experts don't recommend using SSL for email because it’s prone to attacks. TLS, which builds on SSL’s foundation, is the modern standard.

TLS (Transport Layer Security)

TLS was developed in 1999 as an upgrade to SSL, and addresses a lot of its security flaws.

TLS encrypts emails while they are in transit, protecting the data as it flows between web applications and servers.

By encrypting email content as it travels across networks, TLS ensures that data remains private until it reaches its destination.

A common implementation of TLS is STARTTLS, which upgrades unsecured connections to encrypted ones, blocking interception by eavesdroppers.

"While TLS is essential for securing data in transit, it’s important to recognise its limitations. Organisations should think about layering different types of encryption to cover all vulnerabilities."

— Mike Wakefield, CTO, Beyond Encryption

As noted above though, TLS doesn't provide end-to-end encryption.

If emails are stored unencrypted on servers (for example, when they are in people's 'Sent' or 'Inbox' folders), they can be vulnerable to attack.

2. End-to-End Encryption: PGP and S/MIME

PGP (Pretty Good Privacy)

Developed in 1991, PGP was a game-changer in encryption (hence the 'pretty good').

It's what's known as asymmetric encryption, and it involves a public key to encrypt emails and a private key to decrypt them.

Technically, PGP secures email content by combining both symmetric and asymmetric techniques — but the essential takeaway is that it creates a situation where only the intended recipient can decrypt the message.

S/MIME (Secure/Multipurpose Internet Mail Extensions)

S/MIME is an encryption standard that adds digital signatures to emails to verify they are authentic.

Developed by RSA Data Security, S/MIME is built into most major email platforms, making it easy to use in corporate settings.

S/MIME encrypts emails using public-key cryptography and verifies the sender’s identity through digital signatures.

However, users first need to obtain digital certificates from a trusted Certificate Authority (CA).

"S/MIME is ok for enterprise use because it integrates with most corporate systems. But there’s a trade-off: the cost and complexity of managing digital certificates can be high."

— Paul Holland, Founder, Beyond Encryption

3. AES-256: The Gold Standard for Symmetric Encryption

AES-256 (Advanced Encryption Standard - 256-bit) is one of the most secure types of encryption available.

Trusted worldwide, it is used to protect everything from government communications to financial information.

AES-256 uses a 256-bit key to encrypt data, making it virtually immune to brute-force attacks (it would take many, many years to crack).

Only authorised parties with the correct decryption key can access the encrypted content.

• Advantages of AES-256 email encryption:
  • Nearly unbreakable encryption, even with the most powerful computers.
  • Encrypts and decrypts data quickly, making it ideal for secure communications.
  • Works across different platforms without requiring complex key management, simplifying deployment.

"AES-256 underpins many of our secure communication platforms at Beyond Encryption. It strikes the perfect balance between speed and security, making it essential for industries that handle sensitive data daily."

— Adam Byford, CCO, Beyond Encryption

Additional Types of Encryption

Encrypted PDFs and Attachments

Sending sensitive information as encrypted attachments, such as PDFs or ZIP files, adds an extra layer of security.

This ensures that even if the email content is intercepted, the attachments remain inaccessible without the correct decryption key.

This is not the same as a password-protected document in Microsoft Word — which can quite easily be cracked by hackers.

There are various methods of encrypting files and they can use any number of encryption algorithms, some of which are more or less secure.

Web/Client Portal Encryption

Email content is sometimes encrypted and sent to a secure web portal, where it can be accessed by clients or customers.

The drawback of this approach is that people need an account and must log in to view messages, but it reduces the risk by a substantial amount.

This approach is particularly favoured by organisations that need to comply with strict data protection regulations, such as financial services firms or legal practices.

While it can be useful for customers to have an online store of all their communications from an organisation, it is also recommended to deliver content by secure email so that clients don't have to log in every time they receive information from you.

"Customer portals are ideal for regulated industries, where you need that auditable store of communications as a customer and as a business. But without the ability to email securely, in real-time, you lose that immediacy factor."

— Carole Howard, Head of Networks, Beyond Encryption

Understanding Email Encryption

Understanding the different types of encryption is crucial for protecting email communications.

While TLS is a great starting point for securing data in transit, end-to-end encryption methods like PGP and S/MIME offer greater security for sensitive information.

AES-256 remains the gold standard, providing a robust, efficient solution for industries where data security is paramount.

A layered strategy, combining encryption with other security practices, such as strong authentication and ongoing user training, is your best defence against cyber threats.

You can keep your communications safe by staying informed and proactive in relation to digital risks.

FAQs

What Are the Most Common Methods of Email Encryption?

Email encryption includes transport-level encryption (TLS) for securing data in transit and end-to-end encryption (PGP, S/MIME) to ensure only recipients can read the content.

Is Outlook Email Encrypted?

Outlook uses TLS to secure emails in transit but requires additional setup, like S/MIME or third-party tools, for full end-to-end encryption.

What Is the Easiest Way to Encrypt an Email?

Use a secure email service with built-in encryption or set up S/MIME or PGP for advanced end-to-end security.

How Can I Tell if an Email Is Encrypted?

Look for a lock icon in your email client for TLS encryption; for end-to-end encryption, verify settings or encryption keys.

What Type of Encryption Does Outlook Use?

Outlook primarily uses TLS for transit encryption and can use S/MIME for end-to-end encryption with a digital certificate.

What Is the Difference Between AES and RSA?

AES is symmetric encryption, using one key for both encryption and decryption, while RSA is asymmetric, using a public-private key pair for secure communication.

Are All Emails Sent Encrypted?

No, not all emails are encrypted. Many use TLS for transit security, but stored emails and end-to-end encryption often require additional setup.

How Do You Send Files Securely Over Email?

Encrypt files separately (e.g., AES-encrypted ZIPs or PDFs) or use secure portals or encrypted file-sharing services for added safety.

References

Secure E-mail Communications Through Cryptographic Techniques—A Study, Springer, 2020

What is Email Interception?, Beyond Encryption, 2024

Usability of End-to-End Encryption in E-Mail Communication, Frontiers in Big Data, 2021

Advanced Encryption Standard (AES), NIST, 2001

Email Security Issues, Tools, and Techniques Used in Investigation, MDPI, 2023

Managing Access to Confidential Documents: A Case Study of an Email Encryption Solution, MDPI, 2023

Reviewed by

Sabrina McClune, 28.11.24

Sam Kendall, 15.11.24