Comment by phzbOx

I know it's a bit out of subject but I had to do this a couple time, and now, I simply use google app. It gets the job done, have a nice spam filter and more importantly, users are already used with google services. I'm not saying configuring the server with postfix is bad, far from that, but it might be worthwhile to look at google app as it may speed up things for you and your users.