[dns-operations] Queries for earthlink.net not consistently succeeding

[Frank Bulk - iName.com]

It was our e-mail gateways that alerted me to an issue sending e-mail to
earthlink.net.  The e-mail gateways weren't able to obtain an MX or A record
for earthlink.net.

I've tested from my Windows laptop (which is behind an ASA) and from our
*nix server (public IP) and I'm getting mixed results -- our three Windows
DNS servers (behind the same ASA) time out, even after having their cache
flushed.  Five of our own *nix DNS servers behind a load-balancer happily
supply a response, but two others (we control recursive, so providing the
IPs doesn't help) and our upstream DNS server (167.142.225.5) just time out.
Google's DNS is fine, but 4.4.4.2 doesn't respond.  I'm testing by doing
"dig A earthlink.net @<DNS IP>"

Any ideas what's going on?

Frank