I'm testing out a way that myself and a few others could use S/MIME for our email traffic. I'm using Outlook 2016 with Win10. I have generated my test certificate with the following command in PowerShell:
New-SelfSignedCertificate -Subject "CN=IansEmail" -KeyUsage DataEncipherment,KeyEncipherment,NonRepudiation,DigitalSignature -SmimeCapabilities
I then export this certificate to a PFX file using the MMC Certificate snap-in. Then I:
1) Open Outlook
2) Navigate to File -> Options -> Trust Center -> Trust Center Settings -> Email Security
3) Click on Import/Export and select my certificate
4) Enter the password for my PFX file
5) A dialog pops up that says "This app needs to create a cryptographic key". I uncheck the "Require a password with this key" and hit Ok.
6) Still on the Email Security dialog I check "Encrypt contents ... " and "Add digital signature ...". I then click "Settings" under "Encrypted email heading" and click the "Choose" button next to "Signing Certificate". Upon doing so I see a message that says "No certificate available".
What am I missing?