Email encryption

How to encrypt Outlook emails in transit

Microsoft Outlook is the most popular form of business email, so its users need to know how to share emails securely. That requires encryption for emails in transit to ensure that only those sending and receiving can access messages and files.

Here are the ways to encrypt Outlook emails in transit. 

Encrypting with S/MIME

Outlook allows for S/MIME (Secure/Multipurpose Internet Mail Extensions) encryption where both the sender and recipient use digital signatures to confirm the sender's legitimacy. However, it requires both the sender and the receiver to have an email system supporting S/MIME. 

For Outlook users, setting up S/MIME looks like this:

  1. From the File menu, select Options 
  2. After selecting Options, navigate to the Trust Center option and then Trust Center Settings
  3. Within those settings, click on Email Security
  4. Choose Encrypted Email, and click Settings 
  5. Under Certificates and Algorithms, click Choose and select S/MIME Certificate  

After setting up S/MIME within your Outlook email system, you can activate it within the email message:

  1. Compose email message and add desired attachments
  2. In the message, click Options, then More Options, then Security Settings
  3. Once the Security Properties message appears, click Encrypt Message Content and Attachments
  4. Finish message composition then send to the receiver 

If the recipient has S/MIME activated and uses Outlook, the email message decrypts automatically.

Encrypting with Microsoft 365 message encryption

Businesses subscribed to Microsoft Office 365 can take advantage of the Microsoft 365 Message Encryption feature available. Once subscribed, encrypting a message looks like this:

  1. Begin composing an email message and add desired attachments
  2. From the message, click File then Properties 
  3. Select Security Settings, then click Encrypt Message Contents and Attachments box 
  4. Finish composing, then send 

You can set up Microsoft 365 Message Encryption as a default setting for all messages using the following process:

  1. In the Outlook app, click File, then Options
  2. From there, select Trust Center then Trust Center Settings 
  3. Go to the Email Security tab, select Encrypted Email, then click the Encrypt Contents and Attachments for Outgoing Messages box

From there, any outgoing emails encrypt using this tool. That, however, requires recipients to have digital ID information to view or decrypt the message. 

Encrypting with Outlook add-ins 

The third way to encrypt Outlook emails in transit is through an Outlook Email Encryption add-in. That allows any users, regardless of license type, to activate email encryption and do not require any additional installations by the recipients. 

To encrypt using an Outlook Encryption add-in, users must follow these instructions:

  1. Install the Encryption add-in from the add-in's website or search for the add-in on the Outlook add-ins store. Users can access the add-in store from the Home tab in Outlook by clicking Get Add-ins, or File then Manage Add-ins. Once installed, a Secure Send button appears on the top of the email message window.
  2. Compose email message and add desired attachments 
  3. Instead of clicking Send, select the Secure Send button 

Depending on the encryption software provider, users may have the option to require passwords for email decryption or set time limits on email messages. 

Securing Outlook emails in transit is a good start, but it does not guarantee the security of your data. Explore our email encryption hub and learn how to fully protect your business.


How do I encrypt data in transit?

Encrypting email data in transit varies depending on the email system and encryption software used. Most encryption can be activated in the email security settings and allows users to make it a default setting for all outgoing messages. 

For single-message encryption, the encryption options are in the File, then Properties button of the email message window, where users can choose a check box or set for encrypting that specific message and its attachments. 

How do I enable encryption in Outlook?

To enable Outlook encryption using S/MIME or Microsoft 365 Message Encryption, users must go to File and click Options. From there, select Trust Center, then Trust Center Settings, and go to the Email Security tab.

  • For S/MIME, click on Settings from the Encrypted Email button, and under Certificates and Algorithms, select S/MIME certificate.  
  • For Microsoft 365 Message Encryption, select the box that says Encrypt Contents and Attachments for Outgoing Messages. 

Enabling encryption using an add-in requires varying steps for installation and enabling encryption, depending on the software provider. Be sure to consult with them to get encryption enabled. 

Are emails secure in transit?

Not necessarily. For Outlook, users can set up a default option for sending all outgoing emails encrypted, but it requires them to configure those security features in the email settings.    

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