I've recently installed an Ironport S-160 WSA into our infrastructure and am having problems with Sharepoint uploads. Our SP servers use IWA authentication to allow users to upload images and couments hosted in a DMZ outside of our domain. What I've discovered is that if you try uploading an image \ document over 40kb, the connection times out. For the moment we can get around the problem by adding the site to the proxy bypass list inside IE but it would be good to be able to program the S-160 to accept the tarffic without failing. If I set the authentication scheme from NTLMSSP to Basic, the connection works, the only problem is this means that domain user credentials would be transmitted in clear text over the internet (not a good idea!)
This link gives a description of a similar problem: http://serverfault.com/questions/101127/couldnt-upload-files-to-sharepoint-site-while-passing-through-squid-proxy
I've spent two weeks trying to find a solution so any help will be greatly appreciated!