sendmail connection stuck at DATA

Hi,

I'm running sendmail 8.14.2 on a Slackware system.

I've been noticing a particular connection to my company's
server that is *always* stuck at the DATA transmission
procedure. When I tcpdump the connection, I get something
being sent and then it hangs there. I've disabled all
the filters, and it still doesn't seem to do anything.
I would then get subsequent connections from the same
ISP that would also hang at the DATA part. I know it is
a valid system coming in because the other party is
using that ISP and whenever they send attached files,
I get this strange phenomena. Now, my server gets
so many subsequent connections that it is refusing
other connections. In a sense, I'm being DOSd
by a valid connection.

Can anyone suggest a possible way to solve this issue?

Thanks.

Ed