Multistreaming allows you to archive multiple mailboxes in parallel.
User Mailbox and Journal Mailbox: Each access node that is associated with the Email Archiving App can have a maximum of 20 streams for each job. However, one service account can only use a maximum of 15 streams regardless of the value set for the subclient. If you need to use a higher number of streams, use more than one service account.
In the navigation pane, expand Solutions > Exchange Apps, and then click the Email Archiving App.
On the upper-right corner, click on Settings.
On the page that appears, in the General area, click Edit.
The General dialog box appears.
In the Max streams box, enter the number of streams that you want to use.
If you do not want to archive multiple mailboxes in parallel, enter a value of 1.