Batch PTR lookups (up to 20 IPs at once), forward confirmation (FCrDNS), CNAME chain resolution and CDN detection.
PTR only records what an IP calls itself — nothing forces that name's A record to point back, so anyone can publish a fake one. The record only becomes trustworthy when the PTR name is resolved forward and lands on the same IP. That is Forward-Confirmed reverse DNS. Mail servers use it as the first check on a sender's identity, and most receiving systems reject mail that fails it.