In order to setup your Dynamics CRM Email router to work with Exchange EWS Webservices, you should proceed as follows: Configure your CRM email router profile to use Exchange Webservices, either 2007 or 2010. Choose the "Other Specified" option in the Access Credentials dropdown. Then, add permissions to this account so it has enough rights to poll the CRM users’ mailboxes.
Read the original here:
How to setup Exchange 2007 and Exchange 2010 for CRM Email Router