Email encryption in Office 365

 

Applies to: Exchange Online, Exchange Online Protection, Office 365

Topic Last Modified: 2017-03-05

Summary: Compares encryption options in Office 365 including Office Message Encryption (OME), S/MIME, Information Rights Management (IRM), and introduces Transport Layer Security (TLS).

Office 365 delivers multiple encryption options to help you meet your business needs for email security. This article presents three ways to encrypt email in Office 365. If you want to learn more about all security features in Office 365, visit the Office 365 Trust Center. This article introduces the three types of encryption available for Office 365 administrators to help secure email in Office 365:

  • Office Message Encryption (OME).

  • Secure/Multipurpose Internet Mail Extensions (S/MIME).

  • Information Rights Management (IRM).

Encryption is the process by which information is encoded so that only an authorized recipient can decode and consume the information. Office 365 uses encryption in two ways: One is by implementing encryption in the service and the second is by offering it to you as a customer control. In the service, we make use of encryption in the platform, where it works by default and you don't have to configure anything. For example, Office 365 uses Transport Layer Security (TLS) to encrypt the connection, or session, between two servers.

Here’s how email encryption typically works:

  • A message is encrypted, or transformed from plain text into unreadable ciphertext, either on the sender’s machine, or by a central server while the message is in transit.

  • The message remains in ciphertext while it's in transit in order to protect it from being read in case the message is intercepted.

  • Once the message is received by the recipient, the message is transformed back into readable plain text in one of two ways:

    • The recipient’s machine uses a key to decrypt the message, or

    • A central server decrypts the message on behalf of the recipient, after validating the recipient’s identity.

Watch this video for an introduction to Encryption in Office 365.

 

Conceptual artwork that describes OME Conceptual artwork that describes IRM Conceptual artwork that describes SMIME

What is it?

Office 365 Message Encryption (OME) is a service built on Azure Rights Management (Azure RMS) that lets you send encrypted email to people inside or outside your organization, regardless of the destination email address (Gmail, Yahoo! Mail, Outlook.com, etc.).

As an admin, you can set up transport rules that define the conditions for encryption. When a user sends a message that matches a rule, encryption is applied automatically.

To view encrypted messages, recipients can either get a one-time passcode, sign in with a Microsoft account, or sign in with a work or school account associated with Office 365. Recipients can also send encrypted replies. They don’t need an Office 365 subscription to view encrypted messages or send encrypted replies.

IRM is an encryption solution that also applies usage restrictions to email messages. It helps prevent sensitive information from being printed, forwarded, or copied by unauthorized people.

IRM capabilities in Office 365 use Azure Rights Management (Azure RMS).

S/MIME is a certificate-based encryption solution that allows you to both encrypt and digitally sign a message. The message encryption helps ensure that only the intended recipient can open and read the message. A digital signature helps the recipient validate the identity of the sender.

Both digital signatures and message encryption are made possible through the use of unique digital certificates that contain the keys for verifying digital signatures and encrypting or decrypting messages.

To use S/MIME, you must have public keys on file for each recipient. Recipients have to maintain their own private keys, which must remain secure. If a recipient’s private keys are compromised, the recipient needs to get a new private key and redistribute public keys to all potential senders.

What does it do?

OME:

  • Encrypts messages sent to internal or external recipients.

  • Allows users to send encrypted messages to any email address, including Outlook.com, Yahoo! Mail, and Gmail.

  • Allows you, as an admin, to customize the email viewing portal to reflect your organization’s brand.

  • Microsoft securely manages and stores the keys, so you don’t have to.

  • No special client side software is needed as long as the encrypted message (sent as an HTML attachment) can be opened in a browser.

IRM:

  • Uses encryption and usage restrictions to provide online and offline protection for email messages and attachments.

  • Gives you, as an admin, the ability to set up transport rules or Outlook protection rules to automatically apply IRM to select messages.

  • Lets users manually apply templates in Outlook or Outlook Web App.

S/MIME addresses sender authentication with digital signatures, and message confidentiality with encryption.

What does it not do?

OME doesn’t let you apply usage restrictions to messages. For example, you can’t use it to stop a recipient from forwarding or printing an encrypted message.

Some applications may not support IRM emails on all devices. For more information about these and other products that support IRM email, see Client device capabilities.

S/MIME doesn’t allow encrypted messages to be scanned for malware, spam, or policies.

Recommendations and example scenarios

We recommend using OME when you want to send sensitive business information to people outside your organization, whether they’re consumers or other businesses. For example:

  • A bank employee sending credit card statements to customers

  • A doctor’s office sending medical records to a patient

  • An attorney sending confidential legal information to another attorney

We recommend using IRM when you want to apply usage restrictions as well as encryption. For example:

  • A manager sending confidential details to her team about a new product applies the “Do Not Forward” option.

  • An executive needs to share a bid proposal with another company, which includes an attachment from a partner who is using Office 365, and require both the email and the attachment to be protected.

We recommend using S/MIME when either your organization or the recipient’s organization requires true peer-to-peer encryption.

S/MIME is most commonly used in the following scenarios:

  • Government agencies communicating with other government agencies

  • A business communicating with a government agency

For information about email encryption options for your Office 365 subscription see the Exchange Online service description. Here, you can find information about the following encryption features:

  • Azure RMS, including both IRM capabilities and OME

  • S/MIME

  • TLS

  • Encryption of data at rest (through BitLocker)

“Data at rest” refers to data that isn’t actively in transit. In Office 365, email data at rest is encrypted using BitLocker Drive Encryption. BitLocker encrypts the hard drives in Office 365 datacenters to provide enhanced protection against unauthorized access. To learn more, see BitLocker Overview.

 
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