How to Migrate Mail in a collection in On Demand Migrations
In the Project, select the collection you want to migrate.
In the next screen, click "Select Mailboxes".
In the Accounts Screen, click the top box to select all Mailboxes in the collection.
Click Migrate Mail.
On the New Migration Task screen choose the type of Mailbox in the Migration scenario and choose what type of data you wish to migrate.
On the Licensing Plan screen select the licensing plan you wish to use to assign licenses and select the appropriate
Assign the selected plan to unlicensed accounts only. Licensed users will retain the existing plans
Assign the plan to all accounts. Licensed users will be switched to the selected plan
On the Items to exclude windows, select the types of Data you wish to exclude from the Migration as well as enter any folder names you wish to exclude. If require enter date range by adding the dates in the "Exclude mail after" and "Exclude mail before sections:
On the Summary Screen enter a name for this Mail Migration task, and verify your options are correct.
Select "Start the task automatically when the wizard is finished."
Select Tasks to verify this task has started
Once this task is complete select Events to see if there were any errors or warnings during the migration