Recently whe working with a client, we ran into an issue with brutally slow Outlook 2007 performance when running Outlook on Windows 2008 x64 with XenApp 5. The issue occurred whether connecting through the console, RDP, or ICA. All other applications worked fine. Some of you XenApp gurus may have already seen this. When checking the Outlook connection status, we could see average response times of 3000 milliseconds. After some troubleshooting involving removing and reinstalling Outlook, going with a plain vanilla Outlook install with no updates etc. we were still not able to resolve this issue. We did some digging and found various references on google about Outlook being slow on recent OS builds. All indications pointed to a new TCP auto tuning feature. After running -
netsh interface tcp set global autotuning=disabled and rebooting the server Outlook responded great. Now, I haven’t research what the implications are of disabling tcp autotuning, but it certainly resolved our only issue and everything continues to perform well. Hope this helps someone else that runs into this issue!