Sign EML Files with DKIM and Provide setup instructions for DNS

I am looking for a C# component that will sign an eml file with a DKIM signature. I will send in the eml contents in a string, with the sender domain, and location of any keys. You should reply back with a signed version of the eml file. You should include instructions of what needs publishing in DNS. It should be tested with encoded emails, emails with chinese characters in them. If it cannot sign because the email is corrupt it should return the unsigned email.