Why i cant receive the mail

I installed the gitlab on my synology system by docker. But i cant receive the mail. And i cant find the config file in /etc/gitlab. After searching, i find one place ‘/home/git/gitlab/config/initialize/smtp_setting.rb’ that have the smtp info.
So i change this set.
I reatart the gitlab in synology.
But the smtp_setting file turned back. Nothing changed.