The <verb>-MailboxExportRequest and <verb>-MailboxImportRequest cmdlets have been introduced in Exchange 2010 SP1 to simplify the export of messages directly into a PST file from PowerShell. The previous requirement to have Outlook and some other software installed on the exporting computer have been dropped and the whole export process has been moved to the Mailbox Replication Service (MRS). A small disadvantage is that the cmdlets are not available by default as you’ll first need to define the proper permission to your role group.
I can write in detail how to add these permissions, but Microsoft has done this quite well already in this technet article: Add the Mailbox Import Export Role to a Role Group
This command will get you started:
New-ManagementRoleAssignment -Name "Import Export_Enterprise Support" -SecurityGroup "Enterprise Support" -Role "Mailbox Import Export"