I recently had a strange experience at one of my customers. Suddenly the performance of OWA when accessed through their ISA 2006 server was horrible. Using OWA to read messages was possible, but creating a new message with an attachment was impossible. The operation would hang with the message Uploading you attachments indefinitely. After a looking at all the logs, the ISA policies and the IP settings I checked the speed and duplex settings on the NICs. We had recently switched the NICs in this server to troubleshoot another issue. We switched the Internal NIC for the External NIC, by switching the IP addresses and the cabling. I had evidently forgotten about the speed and duplex settings on the NICs, because the Internal card was now set to 100Mbps/Full Duplex and the Extrenal was set to Auto. The settings should have been switched with the rest of the config. After I set the Internal card to auto and the External card to 100Mbps/full everything started working again. Funny how a setting like this can have such an impact. I thought that once the speed and duplex settings were negotiated with the switch it was no longer relevant. There are known issues with mismatched speed/duplex settings.