Use these instructions to import a secure e-mail certificate (.p12 or .pfx) into Windows and configure it in Outlook
Secure e-mail certificate (.p12 or .pfx file)
Password to the Secure E-Mail Certificate
Double-click the certificate file .p12/.pfx
Enter your password to your certificate file .p12/.pfx.
After that click on "Next"
Select the menu item "File" in the upper left corner.
Click on "Email Security"
Select the two checkboxes as shown below.
Click on "Settings".
Enter a name for your S/MIME profile
Mark both checkboxes as shown below
Select the certificate you want to use for signing and encryption.
Change the hash algorithm to SHA256.
Close all windows with "OK".
Create a new message.
Select the "Options" menu item.
Check whether the "Sign" item is activated.
After that, you can send a test message to yourself, for example.
Locate the message you just sent in the Outbox folder and open it.
Click the signature icon on the right
The signature is displayed as valid
Close the window by clicking on "Close".