Migration Manager for Exchange

Exchange to Exchange - mailbox matching

Hello,

We are currently merging 2 Exchange environments.

User X has a mailbox on Server A and Server B. domain xxx.com is forwarded on server A to a contact which points to  the mailbox on server B.

According the documentation, I need to create CSV files in order to match the mailboxes for the sync to work. (i now receive target mailbox not found error)

Can anyone help me with an example of how the file should look like?

Thank you in advance,

Kristof