That gets into a lot of complexity. Using just the native Send-MailMessage, you'd have to construct the signed, multipart MIME body of the message manually, and then PowerShell could definitely send it.
If you're using the .NET Framework's SMTPClient, you might be able to.
$cert = # get a certificate object from the CERT: drive
$smtp = new-object -type system.net.mail.smtpclient