This article will walk you through configuring your PersonalSign certificate in Microsoft Outlook 2013.
Before your certificate can be configured in Outlook, it must be downloaded & installed into your Windows Certificate Store.
https://support.globalsign.com/customer/portal/articles/1216453
https://support.globalsign.com/customer/portal/articles/1211387
Or, you can check the step by step guidelines below.
Check your certificate installation for SSL issues and vulnerabilities.