220.127.116.11.1 Decompressing and Decrypting the Message
To decompress a message, a client MUST obtain the storage container as specified in section 18.104.22.168 by processing the "message.rpmsg" attachment as specified in section 22.214.171.124, decompressing the compressed bits in each successive data block as specified in [RFC1950] and [RFC1951]. If the PidNameRightsManagementLicense property (section 126.96.36.199) is present, the Use License has already been obtained. If it is not present, the client MUST obtain the required Use License from the server by using the publishing license in the container, as specified in [MS-RMPR] section 188.8.131.52.
The client SHOULD<4> then cache the Use License in the PidNameRightsManagementLicense property if the Use License is not already present. A user can open the message offline if the Use License is cached. When the message is opened, the client SHOULD store the Use License in the RMS License store so that the license can be used to open any rights-managed attachments in the message.
By using the Use License, the messaging client decrypts the encrypted content as specified in [MS-RMPR].