RPC over HTTP provides a connection to exchange servers, from outside the organization, without the need of a VPN connection. This is great thing if it works, but very hard to troubleshoot when it goes wrong and even harder troubleshooting somebody else’s server when you have no idea what it is that has changed to break it. I’ll mention a great tool to point you in the right direction of troubleshooting as there is so much which could go wrong and blindly trying it all might even damage your server more. This tool was created by Microsoft and is found at https://www.testexchangeconnectivity.com This is one of the best things from Microsoft. It helps to narrow down the issue to the exact part which is not working correctly. I was getting this message: The connection to the Microsoft Exchange Server is unavailable. Outlook must be online or connected to complete this action. I have had this problem before, but it’s not quite the same problem, so before you spend hours searching or guessing what the problem is, consider running the connectivity test and then pick the solution. My problem of course was not only one, but multiple issues. Easy solutions to this problem:
- Check all required exchange services are started (system attendant etc.)
- Check event log for any errors related to this problem.
- Re-install RPC over HTTP (add/remove windows components)
If any of these worked, then great, if not here is the harder part: Run the RPC over HTTP exchange analyzer, what the results showed for me was issue with the RPC ports. This is very useful tool to set your registry to the correct values http://www.petri.co.il/software/rpcnofrontend.zip remember to restart the server after making the change and backup your registry before, just in case. To check the port settings see following registry keys HKEY_LOCAL_MACHINE\Software\Microsoft\Rpc\Rpcproxy – required ports are 6001,6002 and 6004, strange range of ports up to 5000 was set in my case. Re-running the connectivity analyzer then showed an error with the GAL, which I suspected earlier, but being part of multiple issues this wasn’t resolved as I have reverted my changes back to original. I then remade the change to the GAL permissions, which should be list, read and open address list and the issue was solved!!! The easiest way of all to fix this problem is to migrate the customers email to our new Cloud Email offering and put the SBS 2003 server to rest and no longer have to worry about supporting Exchange.