Being at the end of my tether trying to resolve this, hopefully you guys can help me. Running Windows Server 2003 Std R2 with Exchange 2003 SP2 installed. This is also a DC with AD and GC configured. HTTP over RPC has been working perfectly until a few weeks back when a bunch of Microsoft Updates were installed. One of the updates had hung (cannot remember which one, but I'm sure it was for Exchange) and I'd assumed because it couldn't stop the IMAP service. Anyway, after a reboot I installed this update successfully manually. Since then, HTTC over RPC is kind of working... but it's not.... I have checked all registry/IIS/Exchange settings and as far as I can see they are all correct. Clients are running Outlook 2003 (with some on 2010). HTTP configured clients Outlook will prompt for authentication, then connect using HTTP over RPC (RPC Diag shows it working ok). It will then lose connectivity and state 'trying to connect', then it will connect again. Upon attempting to send mail, it will sit at trying to send. Closing down Outlook and reopening it does actually send the mail. Having tried the Remote Exchange Connectivity Analyser, it showed a few errors, relating to not being able to ping the endpoint 6001. Telnetting to those ports was successful however. Having re-entered the 'validports' registry entry, the Remote Exchange Connectivity Analyser now completes successfully.... but HTTP is still not working. A restart is on the cards for this server but will need to be done out of hours, so I'm hoping that's going to sort it. Any other ideas though?