Our server keeps getting blocked

Hi All,

I am hoping one of you might be able to provide some insight into a problem
we are having with our server.  Our company uses a server which is hosted by
lunarpages.com in the US.  Over the last several weeks we have been having
an unending stream of connection problems.  Access to our website and mail
server keeps coming up and going down (although it stays down more than it
is up).  

I have been doing some research into the issue and this is what I have
discovered:
1.  	The server name is resolving correctly so I don't believe it is a
DNS issue.
2. 	If I go to our site via a proxy server located in a country other
than China there is no problem.
3. 	If I go through an anonymous proxy within China I cannot get to the
server.
4.	The problem is intermittent (sometimes there is no problem, then all
of a sudden we cannot connect, then it will eventually work again)

Additional info:
This problem was getting so severe that we recently changed hosts (now we
are using lunarpages.com).  After the change the problem seemed to have been
solved (with only the occasional connection problem), however, now it
appears that the same problem is occurring.

I would love to hear any ideas as to what the issue may be.  If the host was
being blocked, why would it only work part of the time?  Perhaps it is a
problem with our office server, which functions as a router (IP
masquerading).  However, in the past it has been working perfectly and the
configuration has not been altered anytime recently.  Furthermore I can get
to any other website just not ours. Frustration extreme!!!!!

Thanks in advance,

Ben