Add Certificate on Local Certificate Authority - Outlook

1. First, start up Outlook and get the error message on the screen.


2. Select “View Certificate” > Install Certificate > Next.


3.Selct “Place all certificates in the following store” > Browse > Select “Trusted Root Certification Authority > OK.


4. Finish.


5. Select yes to accept the certificate import> Restart Outlook.

To Push Certificate on All Domain Connected PCs, see the below mentioned MS link 
Distribute Certificates to Client Computers by Using Group Policy | Microsoft Docs