This routine was drafted up for Exchange 2007 - Documenting for archival purposes

To List all mailboxes, use this command at the Exchange Shell:

Get-Mailbox -Database "Exchange2007\Mailbox Database"

To Export to PST Files for Each User, use this command:

Get-Mailbox -Identity "Domain\UserN" | Export-Mailbox -PSTFolderPath E:\PST\ -Confirm:$false

To Execute ps1 batch file use  ".\NameFile.ps1"  the .\ allows execution of the batch

[PS] C:\Windows\system32>Get-Mailbox -Database "Exchange2007\Mailbox Database"

Depending on Server load, you can script these, or run each of the ones below as a single command.

Get-Mailbox -Identity "Domain\AName1" | Export-Mailbox -PSTFolderPath C:\PST\ -Confirm:$false

Get-Mailbox -Identity "Domain\AName2" | Export-Mailbox -PSTFolderPath C:\PST\ -Confirm:$false

Get-Mailbox -Identity "Domain\AName3" | Export-Mailbox -PSTFolderPath C:\PST\ -Confirm:$false

Get-Mailbox -Identity "Domain\AName4" | Export-Mailbox -PSTFolderPath C:\PST\ -Confirm:$false