I got free code from http://www.phpioneers.com/phplist.php3 called validatemail.
the function of validatemail is tests to see if it's a valid email address.

there is line if ( checkdnsrr ( $tld, "MX" ) )

I upload exactly same free code to all my site but

I found checkdnsrr not work on my main site, and work at my mirror site, all my site run on Linux6.2 php-4.0.1RC2
at least, I want to know it is my main
site DNS problem? PHP install probelm? qmail problem? or other problem? other php mysql application on my mian site is fine.
is there any nice one around here give me some advise about it , thanks a lot.