Why reverse DNS matters
Mail servers check the PTR record of the IP address sending to them. Without a matching, forward‑confirmed PTR, your email is much more likely to be rejected or marked as spam. Reverse DNS also makes logs and traceroutes easier to read.
Who controls the PTR record?
Whoever owns the IP address, not the domain owner. For a VPS, set it in your hosting control panel. For a home connection, ask your ISP. Many do not allow custom PTR records on residential lines.