What types of DNS records exist? What is the purpose of a PTR record?

There are different types of DNS records, the main ones are:

• A (Address) — links a domain name to an IPv4 address.
• AAAA — links a domain name to an IPv6 address.
• CNAME (Canonical Name) — an alias for another domain name.
• MX (Mail Exchange) — indicates mail servers for the domain.
• TXT — stores arbitrary text, often used for SPF, DKIM, and other checks.
• NS (Name Server) — indicates authoritative DNS servers for the zone.
• PTR (Pointer) — used for reverse resolution of an IP address to a domain name (reverse DNS).

PTR record is needed for reverse lookup: determining the domain name from an IP address. This is important, for example, for mail servers to verify that the IP indeed belongs to the specified domain, which helps fight spam and increases trust.