The way to encrypt / secure E-Mails in the Outlook client is built in and simple.
In a new email, click on Options-Permissions-Encrypt Only
If this hasn't been done before, you might have to retrieve the available permissions by clicking on Connect to Right Management Servers and get templates first to load the options.
After encryption is applied, this mail tip is displayed on the top of the email:
Recipients will then have to retrieve the email from a Microsoft server. Here instructions about that from Microsoft:
View and reply to an encrypted message without Microsoft 365 using Outlook for PC
If you're not using Outlook with Microsoft 365, your encrypted message will contain a link in the message body.
Select Read the message.
Select how you'd like to sign in to read the message. If your email provider is Google, Yahoo, or Microsoft, you can select Sign in with Google, Yahoo, or Microsoft respectively. Otherwise, select sign in with a one-time passcode.
Once you receive the passcode in an email message, make a note of the passcode, then return to the web page where you requested the passcode and enter the passcode, and select CONTINUE.
If the templates don't show under Permissions try this fix
- Close all Microsoft client apps
- Open Word, then File-Account
- There may be an indication of a "Fix" with credentials needed, click on that button and log in (to the O365-Okta login prompt), if there is no indication, just log out of it. Close Word and open Word log back into the account
- Then opened Outlook, create new email, Options-Permission and the options for Encryption, Confidential, should appear or pressing the Connect to Right Management Servers and get templates should then work.