I got a problem with some users who uses my ispconfig server as a relay for domains that are not hosted on the server ex. firstname.lastname@example.org, can send/relay mails from email@example.com, I think this is a big problem, because it means that the user can relay as any address they want, as long as they are authenticated, I would like that users only are allowed to send email from the emailaddress they use to authenticate against the smtp server. Is this possible ? I have found some thing about a postfix option called "reject_authenticated_sender_login_mismatch" and "smtpd_sender_login_maps", but i can't get it working. I hope someone in here can help.