3.1.5.1.7 LOCK
In addition to the lock types specified in [RFC2518], the server MUST support two additional lock types: transaction, as specified in section 3.1.5.1.7.1, and checkout, as specified in section 3.1.5.1.7.2.
The public folder and mailboxstores support different sets of locks:
The mailbox store only supports transaction locks.
The public folder store supports transaction-local, write-exclusive, as specified in [RFC2518], write-shared, as specified in [RFC2518], checkout-exclusive, and checkout-shared.