hello. this is something i have wondered a long time now. i have had several different mail servers in the past. also some older plesk servers. when a customer sent an email, the ip of the sender was that of my server. which was ok by my standards. now, with plesk 9.5.4 and postfix, when a customer sends an email through :25 (with smtp auth) the ip of the sender is his own. when i read the headers of such mail, his public ip shows up, instead of the public ip of my server. this ends up with big problems, because many of my customers are small business or private persons, with dinamic IPs that are blacklisted in many places because of the bad politics of spanish ISP (they re-use blacklisted IPs without "cleaning" them first) and so they lose many emails because of antispam systems. how can i change it so all outgoing email for a certain domain uses my servers ip instead of the end-users ip?