I currently have a hp proliant server running on windows server 2003 that acts as my proxy server. i recently aquired a new server that intend to use as my proxy server as the old one is now overwhelmed. I have windows server 2008 r2 running on in and microsoft threat management gateway. My problem is that ever since we switched over to the new server, any email that has attachments bigger than 20kb is not delivered to us. I've reverted back to the old server and normal email flow has resumed. What could be the cause of this?