...

my $number_of_emails_per_minute = 100;

..

my $time = time();

my $count = 0;

while(WHEREVER YOUR ADDRESSES ARE COMING FROM)
{

   # do whatever you do to send mail
    
   $count++;

   if ( $count == $number_of_emails_per_minute )
   {
      my $time_left = 60 - ( time() - $time );
      sleep $time_left;
      $time = time();
      $count = 0;
    }
}