Postfix "Fixing"

My learning continues with OpenSUSE. Now I need help with the following “problems”.
I have a mix of OpenSUSE and Windows computers in my network, all behind a firewall (Sophus UTM) that uses VPN (through an ASUS router) to access the Internet.

My question is:
How do I configure Postfix (with TLS) in Yast2 so OpenSUSE 42.3 sends mail to a specific e-mail address? How can I verify that it is sent from my computer?
I’ve tried to configure, but it do not work for me. A Terminal install and configuration are OK to.

How do I do, all configuration tips and referrals are needed and appreciated?

/ Roland