Email headings in Mail

An individual that I forward email to (Windows user) is complaining about the extraneous message headings on my emails and wants me to delete them. I want to preserve this heading option to view previous addressees for record purposes. Is this something I can adjust in Mail Preferences, or should he adjust it on his end? For some weird reason, he is printing out all email correspondence (waste of paper/ink) destined for his wife's viewing, since she doesn't see text on computer screens very well.

Thanks