And my latest insight:
I ran a PHP testscript from both server B and server C about server B which look sas follows:
<?php
ini_set('max_execution_time', 0);
ini_set('memory_limit', -1);
$host = 'SERVER.B.DOMAIN';
$ports = array(21, 25, 80, 81, 110, 143, 443, 465, 587, 2525, 3306);
foreach...