Resolution
How do I export the EmaMappings.tab file during a large mailbox migration?
fact
Exchange Migrator 2.2 SP1
fix
Although the Exchange Migrator (EM) MMC interface is not available for use during a mailbox migration, you could use the following workaround. The following workaround is possible because the mapping file that EM creates in the database is actually written to, prior to the mailbox data migration. This means if there is a way to pull the information from the database, you can have the EMAMmappings.tab file available before the data migration is complete.
How do you extract the information while the Exchange migration is in progress?
You can use Microsoft Terminal Services to logon to the EM console from another workstation. Open EM, right-click the project, and click Export Migrated Objects. All you need is access to logon to the EM console from the remote machine. You will want to wait until the migration process completes the 'MAKE MAP File' process and begins copying mailboxes before exporting the mappings.