I'm an author of The Bat!
This email client for Win32
that has S/MIME implementation based on own codebase written from
scratch on Delphi as well as the rest of The Bat!
I would like The Bat! to pass interoperability testing while forum
continues. Your help would be appreciated.
The Bat! official releases do not have S/MIME support yet, but beta
versions of The Bat! are S/MIME enabled.
You may download The Bat! with S/MIME support from
RIT Research Labs http://www.ritlabs.com/