Well, you're code's pretty rough, but i'll try and pinpoint the immediate problem:

write STDOUT if defined($registrant and $admin and $tech and $billing 
+and $names[2] and $expires);
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If the above test evaluates to true, you should also exit the OUTER loop, thus;

if defined($registrant and $admin and $tech and $billing and $names[2]
+ and $expires){
  write STDOUT;
  last OUTER;
}
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Otherwise the loop will keep on recurring and print your results several times.

I would also suggest that a much better way of doing this would be to take the test out of the loop entirely.
Also, you may want to take a look at the Net::Whois module.