If possible, reduce the amount of data to be migrated. You can
reduce both directory information and mail data. There are many
ways to accomplish this, including the following:
Purge your existing mail system of out-of-date files before you
begin the migration; for example, by running a disk check.
Instruct users to delete old mail and calendar data.
In Migration Wizard, you can do the following:
Be sure that user accounts that you do not want to migrate are
not selected on the Account Migration screen.
Set a time window for data you want to migrate to the
information store using Dated From on the Migration
Information screen.