https://support.google.com/mail/troubleshooter/2920052?hl=en
Also make sure a DMARC record is setup.
DMARC is enabled (and in one of the screenshots, Google shows it passing). I get reports from them, but it provides no insight into their decisions.
[1] http://mxtoolbox.com/diagnostic.aspx
https://support.google.com/mail/troubleshooter/2920052?hl=en
Also make sure a DMARC record is setup.