Nice and simple PowerShell one-liner to create mailboxes for everyone in an Active Directory Organisational Unit (useful for Mail-enabling a few hundred Student accounts in one hit).

On your Exchange server, open the Exchange Management Shell and run this command

Get-User -OrganizationalUnit "OU=New,OU=Students,DC=Contoso,DC=com" | Enable-Mailbox -database "Students"

Easy.