There has been much talk in the media recently about using email encryption to avoid surveillance and monitoring. In this article we help you understand what email encryption is, how it works, and the options that are available to you as a Runbox customer.

Summary of this Article

• Email communication involves at least a sending email client, a sending email server, a receiving email server, and a receiving email client.
• Email communication between client and server is typically encrypted using basic encryption methods such as TLS or SSL.
• In addition to this, you can use end-to-end encryption with any email service — and we show you how to use encryption with Runbox.

First, the Basics

In order to understand how email encryption works, we need to cover the basics of email communication. Don’t worry, we’ll keep it non-technical and it’s pretty simple.

To send an email to someone, 4 things are usually needed (in addition to the Internet itself):

1. A sending email client such as Outlook, Apple Mail, and Thunderbird.
   An email client is a program or app, which is running on a computer, tablet, or smart phone. When you use a webmail service such as Runbox Webmail, your browser acts as the email client. Whatever it’s called, it’s the program you use to write your email messages.
2. A sending email server such as Runbox.
   When you use Runbox your email client connects to our servers, which takes care of figuring out where on the Internet the recipient is located. More correctly, it looks up the domain name part of the recipient’s email address and connects to the servers responsible for that domain name.
3. A receiving email server such as Gmail.
   The receiving email server accepts the message and stores it until the recipient downloads it to her email client.
4. A receiving email client such as Outlook, Apple Mail, and Thunderbird.
   Similar to the sending email client, the recipient uses an email program to send and receive email. The email client regularly connects to the receiving email server to check for new email, and usually keeps a copy of the messages on the server so that they are available to other devices the recipient may be using.

Standard Email Encryption

The email communication between the client and server (#1 and #2 above) is already encrypted by default if you are using the recommended settings. When using Runbox Webmail encryption is always enabled, which you can tell by the padlock in the address bar and the web address starting with “https” (where the “s” stands for secure).

This type of encryption is called Transport Layer Security or TLS for short (which has succeeded Secure Sockets Layer, SSL) and protects your data from being eavesdropped on its way from your email client to our servers.

After accepting the message for relay, the Runbox outbound email server then looks up the email service responsible for the recipient’s domain name and connects to one of their servers. Runbox always attempts to establish an encrypted connection using TLS, but many services do not support such connections yet.

After connecting to the receiving server (#3 above), Runbox hands over the message for further processing.

The final step (#4 above) between the receiving email server and the recipient is usually encrypted, but it depends on the encryption support of the receiving email service’s servers and the settings in the recipient’s email client. More details: Secure Transfer of Email

Why this type of encryption isn’t sufficient

In other words, there is no way of knowing whether the communication is actually encrypted all the way from you to the recipient. Although some email services provide encrypted email storage, this doesn’t resolve the problem of unencrypted connections further down the message’s path.

In the event that someone was able to eavesdrop on communication encrypted using SSL/TLS, they would in principle not be able to decrypt the contents without somehow accessing the private encryption key which is only stored on the provider’s servers (unless Perfect Forward Secrecy was implemented, which is the case with Runbox).

However, this type of encryption is still theoretically vulnerable to surveillance because the encryption standards used have been developed in cooperation with US intelligence agencies, although any such weakening has been denied by NIST (National Institute of Standards and Technology).

End-to-end encryption of email

The best solution available is to add another layer of encryption on the email communication all the way from sender to recipient. This is called end-to-end encryption and is already available for use with virtually any email service or provider.

When using end-to-end encryption, the contents of messages will be unreadable to a potential eavesdropper all the way from sender to recipient. It is of course always important that the two parties take great caution to secure their computers or devices to prevent them from being compromised.

Note that the metadata (sender and recipient addresses, subject line, timestamp, etc) of email messages is always unencrypted in order for the message to be routed to its recipient.

There are two main email encryption standards available: PGP and S/MIME. This may look cryptographic in itself, but we will explain both of them. Runbox supports both standards, which can be used with an email client or with Runbox Webmail.

See Encrypting Your Runbox Email for an overview of email clients and their encryption support.

PGP: Pretty Good Privacy

Despite the name, PGP is considered to be cryptographically very strong and is probably the most popular email encryption standard today.

PGP is the easiest encryption standard to get started with because it doesn’t involve anyone but the sender and recipient of a message. It is based on a “web of trust” because it only involves the sender and recipient and assumes that they trust each other.

• Both parties must have a PGP enabled email client or webmail service.
• The sender must have generated a private/public encryption key pair using software that is downloaded and installed locally.
• The recipient must have downloaded the sender’s public key, because the recipient’s public key is used by the sender to encrypt the message. The recipient’s private key is used to decrypt the message.
• Can be used with webmail services with a web browser.

To get started, see our Encrypting and Securing Email Using OpenPGP help page.

S/MIME: Secure/Multipurpose Internet Mail Extensions

S/MIME is a standard being adopted by the IETF (Internet Engineering Task Force) and requires some more preparation on the part of the email user.

• S/MIME functionality is built into most major email client programs.
• Both parties must have an S/MIME enabled email client.
• A certificate must be obtained from a Certificate Authority and installed in the sender’s email client.
• Is based on a “chain of trust” because the Certificate Authority validates the sender’s identity and makes the public key available to others.
• Is not suitable for use with webmail services using a web browser.

We hope this article helped you understand how email encryption works and how to get started using it. And as always, please contact us if you have any questions.

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