title: Docker container EXIT IP on system with multiple ip aliases and gateways, iptables iproute2
body: <p>I have a gentoo system with multiple ip addressess and default gateways on same interface. I have a docker container as mail server. </p>
  
  <p>But I found, that mail server is not sending mail from the ip, that was passed with <code>-p</code> command, but from first ip in interface. That way, mail is not delivering as there is no PTR/SPF records about this ip.</p>
  
  <p>How to specify an exit IP address for docker container?<br>
  I have configured all with iproute2.</p>