IP used in the HELO request

Hi,

I use Post SMTP with the Google API on all the sites we maintain and test the configuration using mail-tester.com.

Since the re-launch of Post SMTP (when Postman SMTP was replaced), I’ve had clients complaining about not getting emails, so I run the test on mail-tester.com and I get:

“IP used in the HELO request
The hostname should be a domain name, not an IP address”

Which lowers the score by 4 or 5 points.

On a couple of sites, I replaced Post SMTP with WP Mail SMTP and reconfigured the Gmail API, after this, the test score goes back up to 8/10 to 10/10.

Is this an issue with the plugin? all sites are on different hosting providers and have different mixes of themes and plugins so the only thing that is a common factor is Post SMTP.

Thanks!