During a recent Exchange server move I ran into some issues with the Microsoft Dynamics CRM Email Router throwing up errors
#26090 – An error occurred while opening mailbox email@example.com. System.Net.WebException: The operation has timed out at System.Net.HttpWebRequest.GetRequestStream()
The error is pretty annoying because of the fact that it doesn’t give you a clear indication of what the problem is. So after checking numerous setting on the router and doing a lot of searching it turns out that this can be attributed to the virtual directory security settings on the Exchange box as outlined in the following Microsoft kb article..
The virtual directories on the Exchange and ExAdmin directories need to be set on Windows Authentication.
I hope that this will save you some time if you have the same problem.