How to get postfix send mail (with Gmail smtp) under macOS Catalina?

I have tried everything (I guess), such as writing my sasl_passwd and editing main.cf in the /etc/postfix folder (as described in [1] ). I also copied my LaunchDaemon plist with a different name to my /Library/LaunchDaemons folder (as described in [2] ). While those people managed to get postfix to send smtp Gmail messages from their terminal under Mojave and El Capitan, respectively. I haven't managed to get their solutions to work under Catalina. Any suggestions?