I have seen maybe two threads about this but never understood them. I followed the Perfect server tutorial for Centos 6.3 I have my own DNS server so after i did the tut i turned off BIND. I also want to make sure my ISPConfig 3 knows its not a Mail server either. Where i see it get tricky is i want to use my MS Exchange server fully for all sending and receiving but i still need to be able to send mail with php on my sites still passing through MS Exchange. I was told in the past to do something with SMTP. Does anyone have detailed steps i could follow to get this done?