In some environments, the Exchange server response times can be very slow due to network connectivity or performance issues.
This is more often the case when dealing with hosted Exchange services.
To extend or reduce the timeout of each Exchange web service request, two advanced App.Settings can be configured.
To know how to create an App.Settings file to enable advanced options, see http://kb.omni-ts.com/entry/304/.
To modify the timeout while resolving the mailbox during the authentication, set this advanced option:
Ews.ResolveTimeout = 30000 (default - 30 seconds)
To modify the timeout used for all other requests, set this advanced option:
Ews.ServiceTimeout = 100000 (default - 1 min 40 seconds)