Code: 1. 2. 3. 4. INTERNET <==>| IIS-SMTP |<==>| PF/RELAY/SPAMCNTRL |<==>|EXCHANGE | PF/IMAP/SQ ADmember Postfix MX? MX? iis.domain.com postfix.domain.com mail.domain.com Hi, Above is my mail config. It's not exactly the ideal situation(...). 1, 2 & 4 are working, and dealing with loads of mail, so there's no problem. Part 3 has to take part to fight spam, and control and visualise amounts (mailgraph). There are a few things I can not find any answers for, so hopefully someone can help me out. - The easiest way would be to just relay all mail with destination domain.dom in the order 1->2->3->4; - The reply order should be 4->3->2->1; 1. How do I have to configure the relay part? After reading many pages I concluded that user (ie. SMTP address) authentication is nessessary for Postfix, otherwise it will just not work. Is this a fact? There is an easy way to configure authentication with a perl script to check all Active Directory SMTP addresses: http://www-personal.umich.edu/~malth/gaptuning/postfix/ 2. With the method discribed above I managed to replicate this in a test environment from 1 - 4 without a problem. Internet in the test environment is in this case another Postfix/CourierIMAP/Squirrelmail server with a few fake domains. 3. The problem starts when I reply as an Exchange user. The message stops at point 3 with the message: status=bounced (Host or domain name not found. Name service error for name=internet.test type=AAAA: Host not found.) The message is quite logic, because the host does not exist. So here we get to the point. 4. How can I let all mail from 4, relay via 3 to 2? Or, maybe even better, how can I create a transparent relay server?. The extra options I configured for the Postfix server of number 3. Code: mydomain = test.lan myorigin = $mydomain #relay_transport = smtp:[testiis.test.lan] relay_domains = test.lan relay_recipient_maps = hash:/etc/postfix/ad_users hash:/etc/postfix/ad_users2 hash:/etc/postfix/pf_users show_user_unknown_table_name = no I know it's quite a story, but I couldn't find another way to tell it. Thanx.