How to configure gitlab docker to use the host's postfix?

I have the gitlab/gitlab-ce:latest docker image and I want to configure E-Mails. Right now I’m not getting an E-Mail if I create a new user. I want to use the postfix which is installed on the host. I tried different settings from this guide, but nothing was working. Can someone help me to configure my gitlab docker to use the postfix on my Debian 9 host?