I really don't think the platform matters at all. This just isn't a "windows" vs. "<platform of choice>" question. Basically, it sounds to me like you need to parse the email body and feed it to encrypt()/decrypt(). You're either going to need to figure how how to do that (see perlretut
and things like that); or try to get a co-worker to do it. If you're looking for a windows specific tool (other than Perl I guess), this just isn't the right site.
UPDATE: It sounds like you don't need Perl, you need a windows email tool. This just isn't a Perl question I guess.