Is it possible in Chilkat to generate a from address like From sender@domain.com on behalf of Andy Kirk <andy@domain.com>
Use the AddHeaderField method to add the "on-behalf-of" header
You might want to review Best practices: Sending email on behalf of users as well as Configure DomainKeys Identified Mail in your DNS and code which can be done by Add DKIM-Signature Header to MIME / Email