In the past I had no trouble sending email to any server even on a shared IP. However, lately I've noticed some of the really large providers have their servers set to not allow email from domains that do not have PTR's.
WHM does not create PTR's by default. I may present this to cPanel also for a possible upgrade in furture versions.
Fortunately, since my network move I have all my domains on IP based Hosting.
I have never set PTR's in the past so when I added them to my DNS I hope I did them correctly. In WHM I simply went into edit DNS, chose the domain, selected PTR, then added the IP on the left and the domain on the right with a full stop on the end.
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