Open Outlook (desktop app or web).
Compose a new email or open a draft.
Click Options (or select the encryption/security option in the compose toolbar).
Select Encrypt (or Encrypt with Microsoft 365 Message Encryption).
Choose one of the following:
Encrypt and allow recipients to view the message (default)
Encrypt and require recipients to sign in (if prompted)
Add recipients and subject/body content.
Click Send.
If prompted, choose the authentication method (send a code/link to recipients) and confirm.
For replies/forwards, use the same encryption setting in the reply window (or let Outlook apply the original protection automatically).
If prompted by your organization, ensure you have the required permissions and that your account is enabled for message encryption.