How Siebel CRM Desktop Processes Activities
Siebel CRM Desktop uses the following types of objects to process an activity:
A native Outlook item, such as a calendar entry, an email, or a To Do item
A Siebel CRM activity record in Outlook that Siebel CRM Desktop synchronizes from the Siebel Server
A Siebel CRM activity record on the Siebel Server
The following image illustrates the relationships between Outlook items in Outlook, Siebel CRM records in Outlook, and Siebel CRM records on the Siebel Server. Multiple activity types map to the Display In value of the Activities Only list. For example, demos, and so on. For brevity, the image does not include these types of activities.

Explanation of Callouts
As shown in this image, Siebel CRM Desktop does the following work to process an activity:
An activity is created in Outlook. For more information, see How Activities Are Created or Modified.
Siebel CRM Desktop adds a record as a Siebel CRM activity in Outlook.
If the user marks the Outlook calendar entry, email, or To Do item as shared, and then saves and closes this item, then Siebel CRM Desktop immediately creates the Siebel CRM activity in Outlook.
During synchronization, Siebel CRM Desktop maps the Siebel CRM activity in Outlook one-to-one with the corresponding activity in the Siebel database on the Siebel Server. If the user shares a new Outlook item or creates an activity in Outlook, then Siebel CRM Desktop uploads this activity during synchronization to the Siebel Server and inserts it in the Siebel database. For more information, see How Siebel CRM Desktop Creates Corresponding Native Microsoft Outlook Items.