MAPI Properties

Description: Contains the number of unread messages in a folder, as computed by the message store.
Property ID: $3603
Property type: PT_LONG
Area: Folder

This property computed by the message store is used for two different, though related, purposes. On a MAPI folder object, it contains the number of messages in a folder. In a heading row in categorized MAPI tables, it contains the number of unread non-associated messages in the category corresponding to that heading row.
This property contains the number of messages in the folder contents table for which the MSGFLAG_READ flag is not set in the PR_MESSAGE_FLAGS (PidTagMessageFlags) property. The PR_CONTENT_COUNT (PidTagContentCount) property contains the total message count for the folder. The PR_CONTENT_COUNT and this property are read-only to clients.
Some client applications display the heading row of a category differently depending on the value of this property. For example, a client can display a category that includes unread messages in bold. This property cannot be used as a category and an attempt to do so results in the MAPI_E_INVALID_PARAMETER value being returned from the IMAPITable::SortTable method.