Storing Data for Solutions
This topic describes using the StorageItem object as a means for developers to store private solution data.
Outlook solution developers often require a place to store and maintain private application data. For example, you may need to store an incrementing order number. The Outlook object model provides the StorageItem object to store this private data.
The StorageItem object represents a thin wrapper on a message object in MAPI (the IMessage object). It is always saved to the associated portion of its parent MAPI folder so that the item is hidden in the folder. It is a child object of the Folder object. This means that solution private data is actually stored at the folder level, allowing the data to roam with the mailbox and be available online and offline.
You can identify a StorageItem object using its subject, message class, or Entry ID. A StorageItem is not tightly bound to only one solution. This allows you to create one or more StorageItem objects in one folder or in multiple folders. Instances of the same solution, or multiple collaborating solutions, can also share the data stored in the private storage.
You can create a StorageItem or get an existing StorageItem to store solution data. You can store the data as an attachment or a value to an item property. To clean up the storage for an application, you can delete the StorageItem objects that it uses, which removes these objects permanently.
The Outlook object model does not provide any collection object for StorageItem objects. However, you can use Folder.GetTable to obtain a Table with all the hidden items in a Folder, when you specify the TableContents parameter as olHiddenItems. If keeping your data private is of a high concern, you should encrypt the data before storing it.