This guide was designed for Office 2016, 2019 and O365

Open Outlook to begin and type the message you want to send along with any attachments. Enter the recipient(s) email address(es) in the "To, Cc or Bcc" Field, these are the email addresses that will have access to open your email. 

**Note - If Email forwarding rules are in place on the recipient(s) mailbox, the new recipient will be unable to open to email as the are not in the required "To, Cc or Bcc" Field**

So here is our email ready to send without "Encryption"

To add the encryption, click on "Option" in the ribbon bar

You will then see the "Permssion" button with a drop down, as shown

There are some a few options to choose from:

But the main option you will use is "Encrypt-Only". This will secure your email and allow the recipient(s) to reply via secure encrypted email too.

Office 365

There is a slight difference in how Office 365 looks to Office 2016 and 2019 - The only difference being that in Office 365 they call the "Permission" button "Encrypt" as shown below: