NAPTR (Naming Authority Pointer) RECORD INFORMATION
A newer type of DNS record that support regular expression based rewriting.
This record set maps the phone number +441632960083 onto three possible identically ordered URIs, with a preference for SIP, then H323, and finally email. In each case, the regular expression matches the full AUS (^.$), and replaces it with a URI (e.g., sip:email@example.com). As this is a terminal record, this URI is returned to the client.Though most NAPTR records replace the full AUS, it is possible for the regular expression to back-reference part of the AUS, to grab an extension number, say:
Once the client has the URI it must be resolved using DNS, but this is no longer part of the DDDS algorithm..
Host can be an @ character (most common) or an alpha-numeric string with periods, hyphens and underscores. Doesn't have to be a Fully Qualified Domain Name (FQDN)
$ORIGIN 18.104.22.168.22.214.171.124.126.96.36.199.e164.arpa. NAPTR 10 100 "u" "E2U+sip" "!^.*$!sip:firstname.lastname@example.org!" . NAPTR 10 101 "u" "E2U+h323" "!^.*$!h323:email@example.com!" . NAPTR 10 102 "u" "E2U+msg" "!^.*$!mailto:firstname.lastname@example.org!" .