XCode Server not sending email notifications to committers whether the build has passed or not
It turns out that a working mail is not enough. You also need mailq to work. See https://gist.github.com/kany/c44c077881047ead8faa for more.

Especially this part if your mailq does not work as it did for me: https://gist.github.com/kany/c44c077881047ead8faa#gistcomment-2254978

Also, you can set up postfix to do proper mail forwarding if you prefer that avenue:


https://blog.anupamsg.me/2012/02/14/enabling-postfix-for-outbound-relay-via-gmail-on-os-x-lion-11/