MailShelf v2 uses both new database structures and new database technologies, which means that manual data transfer from MailShelf v1 to MailShelf v2 is necessary if you wish to continue using your MailShelf v1 data in MailShelf v2.
Ideally, the data transfer should be performed using the MailShelf Archive File Creator, which can be downloaded here.
Further information on data transfer can be found here: