Starts synchronization for a message header.
[in] The number of bytes in the entry ID for the message.
[in] The entry ID for the message.
[in]/[out] Pointer to the HDRSYNC structure for the message header.
Upon IOSTX::SyncHdrBeg, the local store transitions to the download message header state. Outlook initializes for the client the HDRSYNC structure with the current representation of the message header in the store and the parent folder. The client must then download a full message item (as pmsgFull in HDRSYNC). If this was successful, the client also sets ulFlags in HDRSYNC as HSF_OK. Upon IOSTX::SyncHdrEnd, Outlook checks the result in HDRSYNC and uses the information in HDRSYNC to update the local message header.