Microsoft Outlook - Email Encryption


Employees of the City of Round Rock are able to utilize Office 365 Message Encryption (OME) for free. OME is an on-demand email encryption service. With OME, you can send and receive encrypted email messages between users both inside and outside of the City. Office 365 Message Encryption works with Office 365, Yahoo!, Gmail, and other email services. OME helps ensure that only intended recipients can view message content.


  • Send encrypted email messages to anyone, regardless of their email address
  • Provide strong, automated encryption
  • Eliminate the need for certificates and use a recipient’s email address as the public key
  • Communicate through a Transport Layer Security-enabled network to further enhance message security
  • Enhance the security of email responses by encrypting each message in the thread
  • Office 365 recipients get to use an inline experience in supported Outlook clients.

When to Use OME

Use OME to protect sensitive emails that should have extra precautions taken. Examples where OME should be used:

  • Payment Card Industry Data Security Standard (PCI DSS)
    • Credit Card Numbers
    • Account Numbers
  • Personally Identifiable Information (PII)
    • Social Security Numbers
    • Tax Returns
    • Computerized Criminal History

How to Use OME

For any email that has the word “Encrypt” in the subject, we will automatically apply message encryption before it leaves the City. Alternatively, while composing your message, you can select to Encrypt under the Options tab> Permission> Encrypt-Only. 

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This will not deliver the cleartext message to the recipient. They will receive an email that informs the recipient that they have received an encrypted message. Once they save and open the attachment, it will allow them to authenticate with a Microsoft account or use a one time password (OTP).


If they select an OTP, they will receive a second email with a generated number to view the message in a browser. Any replies or forwards from the browser will also be encrypted.





Who can use OME?

  • Any full-time City of Round Rock Office 365 account.

Can internal/external mail systems interact with encrypted messages?

  • Yes

What clients can be used to send encrypted messages?

  • Outlook on the computer
  • Outlook for iOS
  • Native mobile mail apps
  • Outlook Web Access (OWA)

How do I send an encrypted email?

  • Type the word "Encrypt" in the subject. It doesn't have to be at the beginning. It can be at the front, middle, or end of the subject.

How can I test OME?

  • You can send an encrypted email to your personal email to see the process to interact with an encrypted message.

Should I use OME for all my emails?

  • Not unless you want your recipients to take you off the holiday card list. We recommend to use it for external emails that has PII or PCI DSS content.
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