hardcode the smtp_server's IP on keepalived.conf
    
    due to unknown reason (upstream bug probably), keepalived doesn't
    resolve the smtp_server hostname, and instead it tries to connect to
    0.0.0.0:25. By hardcoding the proxy/relay's vIP it solves the issue
    
    https://bugzilla.opensuse.org/show_bug.cgi?id=1076896