PHP Manual: Check DNS records corresponding to a given Internet host name or IP address

bool checkdnsrr ( string $host [, string $type = "MX" ] )

Searches DNS for records of type type corresponding to host.

host: host may either be the IP address in dotted-quad notation or the host name.
type: type may be any one of: A, MX, NS, SOA, PTR, CNAME, AAAA, A6, SRV, NAPTR, TXT or ANY.

Returns TRUE if any records are found; returns FALSE if no records were found or if an error occurred.

Version	Description
5.3.0	This function is now available on Windows platforms.
5.2.4	TXT `type` was added.

Note:
For compatibility with Windows before this was implemented, then try the » PEAR class » Net_DNS.

checkdnsrr