The current implementation of the the Appointments in the Upcoming Appointment feed includes other users appointments if Delegated Access is configured. To disable the population of the Upcoming Appoinments the following custom viaworks index rule can be added:
Override Event Date
<rules>
<rule name="exchange - override event_date" >
<conditions>
<field name="config.connector_type@connector" value="exchange" multiMode="any">
<field name="document_doctype" value="appointment" multiMode="any" />
</field>
</conditions>
<actions>
<remove field="event_date" multiMode="all" />
</actions>
</rule>
</rules>
Please note that the appointments need reindexing after the rule is added for the change to be visible.