I have 2 mail servers . One is external and other is local server . external server domain is "domain.com" and local server domain is "example.com" . All local users are sending mail through local server, but local server is relaying through external server. My problem is , when an email recieving from local users to a gmail user , it shows mail from "email@example.com". But actually its relaying through external server(domain.com). I want to see firstname.lastname@example.org in all mails from local server. Is any idea..? please share it.