Use the Setting class for a delivery extension
The Setting class is located in the Microsoft.ReportingServices.Interfaces namespace and represents information about extension settings for a delivery extension. The Setting class provides infrastructure for storing information about the settings that are required in order for a delivery extension to function properly. For example, in Report Server E-Mail delivery, a user is required to supply settings specific to e-mail delivery, such as the recipient's address, the sender's address, the subject line of the e-mail, and more. Undoubtedly, your custom delivery providers require the user to supply specific settings in order for the delivery extension to deliver notifications and reports.
The Setting class is used when implementing the ExtensionSettings property of the IDeliveryExtension interface. The Setting class is also used for processing the extension setting data that is supplied by a user when a subscription or notification is created.
For an example of how to use the Setting class, see SQL Server Reporting Services Product Samples.