I need to allow WS inside the firewall to connect to a server on the
Internet over port 80. The app involved uses SOAP. It doesn't seem to
work correctly when going through the proxy. The firewall has to be
taken down for the app to work correctly.

I am troubleshooting this second hand so I am not sure if they have to
also remove the proxy from IE to get the app to work or if just taking
the filters down fixes the problem. The vendor claims that they only
use port 80.

I don't know a lot about SOAP. Is there any inherent reason why the
http proxy, working on port 80 would not work for the SOAP protocol?