Why do mail servers need PTR records?

Most receivers check that the sending IP has reverse DNS, and many want it to resolve forward to the same IP (forward-confirmed rDNS).

Who sets the PTR record?

Whoever controls the IP block: your hosting or connectivity provider, not your domain’s DNS host.

Reverse DNS (PTR)

A PTR record is reverse DNS: it maps an IP address back to a hostname. This lookup finds the PTR record for an IPv4 or IPv6 address, which mail servers check before accepting mail from it.

When to use this: Mail from your server is rejected for missing reverse DNS, or you want to know what host an IP belongs to. Command prefix ptr:

About the Reverse DNS (PTR)

Find the PTR (reverse DNS) record for an IPv4 or IPv6 address.

FAQ

Why do mail servers need PTR records?: Most receivers check that the sending IP has reverse DNS, and many want it to resolve forward to the same IP (forward-confirmed rDNS).
Who sets the PTR record?: Whoever controls the IP block: your hosting or connectivity provider, not your domain’s DNS host.