The NAPTR records are not as commonly used as A DNS records, but they have an important purpose: linking servers and users’ addresses in SIP.
What is the NAPTR record?
NAPTR DNS record is a Name Authority Pointer record. It is a type of DNS record that serves to map servers to the users’ addresses in the so-called Session Initiation Protocol or SIP for short. The NAPTR records, together with another type of DNS record called SRV records (service records), allow complex rewriting of rules that provide new uniform resource identifiers (URIs) or domain labels. Depending on the flag of the newly created URI or domain label, it could be used in the following query for a NAPTR record or directly as an output of the entire process for URI mapping.