Briam, here is a sample. (see the Exchange Server Deployment Guide for much more details, especially Appendix B.
http://www.microsoft.com/downloads/details.aspx?FamilyId=77B6D819-C7B3-42D1-8FBB-FE6339FFA1ED&displaylang=en
http://www.microsoft.com/downloads/details.aspx?FamilyId=77B6D819-C7B3-42D1-8FBB-FE6339FFA1ED&displaylang=en )
Mode,exchange
Accounts,c:ntstempaccounts.txt
PostOffice,mig55
Exch55,True
ExchStoreDN,CN=Mailbox Store (MIG-SOURCE-EN),CN=First Storage Group,CN=InformationStore,CN=MIG-SOURCE-EN,CN=Servers,CN=First Administrative Group, CN=Administrative Groups, CN=First Organization,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=mig-source,DC=extest,DC=contoso,DC=com
Container,OU=Test,DC=mig-source,DC=extest,DC=contoso,DC=com
TargetDC,migDC