After calling about fourteen different departments in the Marine Core, trying to get a hold of a technical person to explain the situation, I finally found one today. It seems that the Marine Core has blocked huge sections of the Internet from querying their DNS servers due to "abuse." He couldn't explain exactly what constituted abuse, and that it didn't really matter anyway. Apparently our block of IPs was blocked as part of a much larger block of IPs. More specifically our entire ISP was blocked from communicating with usmc.mil because someone on the same (larger) IP block that we're on was abusing the system. Our entire ISP is blocked for something we didn't do.
Simple enough. Can we remove the block so my customers can use usmc.mil? After a long pause he explained that the only way they can remove an IP block is if the request comes from a sponsoring Marine Core representative. Wow... ok. Since I don't know any Marine Core representatives personally I wanted to see if there was a way I could contact someone and get this squared away for our customers. I was told that they were unable to put me in contact with anyone that could assist in getting the removal processed.
It sounds like we're totally out of luck communicating with anyone @usmc.mil. That means anyone in the Marine Core that has an email address won't work for any of our customers. That means any Marines Core website we're unable to load. All for something we have zero control over.