Postfix in combinaton with MAMP

I'm trying to get Postfix working on my mac but I can not get it working. Operating system is Mojave 10.14.3 MAMP PRO 5.2.2 I use a hostgator smtp which should work. It works anyway in my mail app. I can not find any usable message and I have tried all kind of solutions which I found on internet but it still does not work. By starting postfix in the terminal with "sudo postfix start" I get the message "fatal error". How can I get postfix working on my Mac?