unable to send encrypted email from Outlook

For a Microsoft 365 Family subscription, encrypted mail in Outlook and Outlook on the web relies on Microsoft Purview Message Encryption. When sending or opening encrypted messages suddenly stops working, the documented causes are:

1. The Microsoft 365 subscription in use does not support Purview Message Encryption.
2. The tenant is misconfigured.
3. The signed‑in account is not assigned a valid license for Message Encryption.

Because these are all server‑side or configuration issues, they cannot be fixed from the Outlook client alone and require tenant/account verification and, if needed, support intervention.

To move this forward:

1. Verify that the Microsoft account used with Outlook on the web is the one that owns the Microsoft 365 Family subscription and that the subscription is active.
2. Confirm that encryption is being used from the Options ribbon in Outlook (not from the File > Encrypt dialog), choosing Encrypt or Do Not Forward, as described in the consumer encryption article.
3. If the problem persists across both Outlook on the web and Outlook on the desktop, contact Microsoft support for the account/tenant so they can:
   • Confirm that the subscription supports Microsoft Purview Message Encryption.
   • Check that the account is correctly licensed for encryption.
   • Correct any tenant‑side misconfiguration.

Because the issue has already been identified as server‑side by Outlook for Windows support, the next step is to open a support request specifically for Microsoft 365 account/subscription and Purview Message Encryption so that tenant configuration and licensing can be reviewed and fixed.

References:

• Resolve Microsoft Purview Message Encryption issues
• Send encrypted messages with a Microsoft 365 personal or family subscription