Signed Email w/Exchange 2003, Windows 2003 PKI

Has anyone on this list implemented digital signatures that validate
back to a commercial CA (i.e., Verisign) in an Windows 2003/Exchange
2003 environment?  If so, I'd appreciate any information resources you
can share on the process.  

I've found several documents describing how to configure things for the
users to sign messages once you've setup Certificate Services on Windows
2003, but nothing on how to configure Windows 2003 Certificate Services
to establish a chain of trust to a trusted root Certificate Authority.

Also, if you can suggest a better way for a small (10 users)
organization to do this kind of thing, I'd appreciate it as well.  The
requirements are: a.) must be transparent to the recipient (i.e.,
nothing special required to read the message vs. non-signed email), b.)
must be convenient for the sender (eliminates GnuPG) in a Windows
XP/Outlook 2003 environment, c.) the business principals must have the
means to revoke and manage certificates.


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