Setting up ptr record was answerd in Julie Pelletiers post (you should contact ISP who owns IP you're sending mail from).
Your problem might not be with ptr at all.
First you should know where you're sending email from. Your Google Compute Engine Server? From email server in your office? Are you using a third party's email service? In first two cases, you should have PTR (reverse) record set for IP you're sending email from and value should be hostname of your server. In third case, that company should have PTR and delivery problem might be related to it's reputation or missing/bad spf/dkim records.
Collect more information about your email settings and mail delivery reports (bounced emails and email server delivery logs should provide necessary data) and update your post.