Describes a sub-object restriction which is used to filter the rows of a message's attachment or recipient table.
Type of sub-object to serve as the target for the restriction. Possible values are as follows:
Apply the restriction to a message's recipient table.
Apply the restriction to a message's attachment table.
Pointer to an SRestriction structure.
Sub-object restrictions are not supported by all tables. Typically, only folder contents tables and search results folders support them. For example, sub-object restrictions are used to find a message that has a particular type of attachment or recipient.
For a general discussion of how restrictions work, see About Restrictions.