I'm not familiar with the fastcgi, but try reducing the number of emails that is being sent per minute. You can change that in Universal Email. On your page you should have such variables:
$BurstSize = 10;
$BurstTime = 3;
$WaitTime = 2;
this tells universal email to wait 2 seconds between emails and send a max of 10 emails every 3 minutes. You can try changing those values by reducing the max number of emails that is being sent and increasing the wait time to see if that gives a better result.