By default you cannot see the cmdlets import-mailbox either export-mailbox. To enable the Exchange Management Shell to use these cmdlets you need to run this command to allow a specific user:
New-ManagementRoleAssignment –Role “Mailbox Import Export” –User “Rodrigo”
or you can enable a group:
New-ManagementRoleAssignment –Role “Mailbox Import Export” –Group “MailboxAccessGroup”
After running one of these cmdlets restart the Exchange Management Shell to use the "hidden" cmdlets.