Learn more about .csv migrations
You can generate a .csv file containing a list of mailbox identities from the local database or source forest. Then, you can pipe the content of this file into the script to bulk-create the target mail-enabled users.
For example, the content of the .csv file can be:
EmailAddress
Ian@contoso.com
John@contoso.com
Cindy@contoso.com
For more information about local or cross-forest moves, see Mailbox moves in Exchange 2013, CSV files for Mailbox migration and Manage on-premises moves.