I needed a script to export S/MIME encryption certificates for a client migration. The script requires that the S/MIME private key be exportable. If it isn’t, the certificate can only be recovered at the CA using a Key Recovery Agent (if configured) or Mimikaz 😉
The search routine for the correct certificate may also need to be adjusted, depending on the key usage defined for the S/MIME certificate.
To make the export process as easy as possible for end users, I also built a GUI around it.
https://github.com/tsukaito-code/Powershell/blob/main/Tools/Export-SMIME-Certificate-to-Mail.ps1