If you are going to use the Microsoft Transporter to copy content from a POP3/IMAP4 to Exchange Server 2007, the Exchange Impersonation permission must be done before using the Microsoft Transporter. This permission can be assigned in a specific CAS Server, but if you are going to use a single one you must specifiy it during the wizard. There is an example in the documentation that explains how to apply the permission for all CAS Servers, in this post we will be applying in a single CAS server.
First of all, get the Client Access Server distinguishedname attribute, through the following cmdlet:
get-clientaccessserver | select name,distinguishedname | fl
Now that we have the distinguesdname handy, we can assign the permission using the following cmdlet:
add-adpermission -Identity <CAS distingueshed name> -User <user> -ExtendedRights ms-Exch-EPI-Impersonation
Now, we can move on and use the Microsoft Transporter to copy content from POP3/IMAP4 servers.