Interesting Email Issue

Hey everyone, wanted to see if I could get some help on this.
I have a CentOS VPS running Virtualmin and Postfix for my email server. I am having issues with emails being filtered my gmail on the recipients end. Now here's the interesting part- if I send from my iPhone or from Roundcube webmail it works fine, hits their inbox, and doesnt get filtered. If I send from Outlook on either of my desktops, it gets filtered everytime…
Thoughts?

See original post by blackburn2413