Exchange Processing Wizard is unable to connect to the Exchange server (4281100)

Possible causes:

1.     In an Exchange 2010 environment the EPW needs to connect to the Exchange server holding the mailbox, not to the DAG or CAS.

2.     The name of the Exchange server needs to be specified using the short name (NetBIOS).

3.   When completing the screen which asks which account to use, selecting the account via the "Browse" button might populate the username with "<DOMAIN>\<Display Name> rather than "<DOMAIN>\<username>", so it will fail. Typing the username directly and manually is recommended in such situation.

4.     EPW attempts to connect and authenticate via IIS using HTTP/HTTPS. For Exchange 2007 EPW uses WebDAV, against Exchange 2010 it uses Exchange Web Services (EWS). If or example the Exchange Outlook Anywhere address is not added to the Proxy exclusion list in Internet Explorer, then the authentication is passed to the Proxy server (which knows nothing about Exchange mailboxes) and the call will fail.

Note:  Outlook 2007/2010/2013 uses the Outlook Anywhere address if configured for cached mode. The information is passed from the Autodiscover settings.

When troubleshooting it is a good idea to use NetMon traces to see where the servers are trying to connect. If you notice the proxy server IP then this means the tool is using the proxy when trying to connect to the Exchange server. Check also for any Kerberos authentication errors on both the DC and IIS host and check for a valid Service Principal Name (SPN).