What should you recommend doing before moving the mailboxes?

You have an Exchange Server 2007 organization.
You deploy a new Exchange Server 2013 organization.
You plan to move all of the mailboxes to the new organization by performing a cross-forest mailbox move.
You need to recommend a solution to meet the following requirements:
Users must be able to reply successfully to email messages they received before their mailbox moved.
Users must be able to send email messages to internal mailboxes by using the entries in the nickname cache that existed in Microsoft Outlook before their mailbox moved.
What should you recommend doing before moving the mailboxes?
A. Create a sharing policy and a remote domain.
B. Create an organization relationship and a remote domain.
C. For all of the users in the new organization, add their LegacyExchangeDN value as an x500 proxy address.
D. For all of the users in the new organization, add their LegacyExchangeDN value as an SMTP proxy address.

Correct Answer: C
Explanation/Reference:
Explanation:
Problem:
An email is sent and a NDR is generated to the sender showing an X500 address in the recipient field. The cause of this is that Exchange uses the X500 address to route mail internally and once the attributes have been removed from a user object (or a contact was removed) and a mailbox is created for the same user, Exchange creates a new X500 address (it is the same information as before, but the last three characters are randomized to keep them unique within the system).
Resolution:
The simpliest thing to do is add a new custom email address to the user object, paste the old LegacyExchangeDN in the address field, and set the type to X500.