Open Outlook and start a new email
Go to the Options tab
Select Encrypt
Choose the encryption option you want
If prompted, sign in to your Microsoft account
Send the email
For S/MIME encryption, install a digital certificate first
In Outlook, go to File
Select Options
Open Trust Center
Click Trust Center Settings
Select Email Security
Check Encrypt contents and attachments for outgoing messages
Choose the S/MIME certificate
Save the settings
Compose and send the email
For Microsoft 365 Message Encryption, select Encrypt from the Options tab
Choose the appropriate restriction if available
Send the message