title: Mail going to spam folder from Ubuntu 16.10 postfix
body: <p>I setup postfix on my server, that's subdomain. so main domain and subdomain IP is different. I am sending mail as support@maindomain.com from subdomain.maindomain.com.</p>
  
  <p>Is there any way to avoid the emails going to spam. </p>
  
  <p>Note: Email doesn't show emailed by.</p>