I am unable to Encrypt an email under Outlook

Question

I am not able to encrypt an outgoing email. I am using a E3 license

Answer 1

Hi @Horacio Fernandez 

Thank you for contacting the Microsoft Q&A forum.  

To better understand your situation, may I clarify the following? 

1/ When you mention encrypted email, are you referring to the encryption options available when composing an email in Classic Outlook? 

If so, could you share which option you selected from the choices shown in the image? 

2/ Or are you using S/MIME encryption?

3/ Do you receive any error message when you try to encrypt the email? 
If yes, please share the message with me through the private message. 

Please check your inbox for an email with the subject “New private message on Microsoft Q&A question” to review my response, and look for “View message” in the banner above the post to access the private message chat. 

4/ Does the issue also occur when using Outlook on the web? 
Knowing this helps determine whether the issue is specific to Classic Outlook or related to an encryption policy. 

Your additional insights will help me better understand your situation and provide more accurate guidance.  I look forward to hearing from you soon. 

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Answer 2

With an Office 365 E3 license, Outlook supports two encryption methods: Microsoft Purview Message Encryption (IRM-based) and S/MIME. In classic Outlook for Windows, use these checks and steps:

1. Confirm encryption is available for the account

• A qualifying Microsoft 365 subscription (such as Office 365 Enterprise E3) is required for Microsoft Purview Message Encryption.
• If the tenant or mailbox is not enabled for Purview Message Encryption/IRM, only S/MIME will be available after it is configured.

2. Try encrypting with Microsoft Purview Message Encryption (classic Outlook)

• Create a new email.
• Go to Options > Encrypt.
• Choose an option such as Encrypt or Do Not Forward.
• Finish composing the email and select Send.
• If Encrypt does not appear, the account may not be configured for Purview Message Encryption; in that case, use S/MIME.

3. Set up S/MIME in Outlook (if Purview encryption is not available)

• S/MIME requires a personal certificate installed for the account and S/MIME configured in Outlook. Follow the steps in Set up Outlook to use S/MIME encryption and digital signatures for classic Outlook.
• After S/MIME is configured, encrypt a single message:
  1. In a new email, select Options > Encrypt.
  2. Choose the S/MIME-based encryption option (for example, an option that enforces restrictions like Do Not Forward if exposed via S/MIME policy).
  3. Send the message.

4. Ensure the recipient can be encrypted to

• If encryption fails for a specific recipient, the recipient’s public key may be missing (for S/MIME). For internal recipients, the public key is normally in the GAL; for external recipients, exchange signed mail and install their certificate before encrypting.

5. Check for conflicting protection types

• IRM-based Purview Message Encryption must not be applied to a message that is already signed or encrypted with S/MIME, and vice versa. Remove any S/MIME signing/encryption before applying IRM, or remove IRM before applying S/MIME.

If the Encrypt button is missing entirely even with E3, the tenant admin must verify that Microsoft Purview Message Encryption/IRM is enabled and that S/MIME is configured for the organization and client.

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References:

• Send S/MIME or Microsoft Purview encrypted emails in Outlook
• Learn about securing and protecting email messages in Outlook
• Set up Outlook to use S/MIME encryption
• Security and compliance in new Outlook for Windows
• Why can't I encrypt?
• Send a digitally signed or encrypted message for Mac