Hello Tom,
Inbound ISP_D* queues will be created as a result of inbound CSA* queues which in turn are created whenever there's an edit made in activities, BPs etc.
After that filter conditions are read from table CMWC_MBA_FILTER which is mapped to the SPRO setting IMG under CRM->CRM Middleware and related Components->Server-Based Groupware Integration->Settings for Contacts (Business Partners)->Filter Condition for Business Partners Exchange with Groupware, and accordingly the data is sent to the Groupware site in the form of a queue ISP_OXXXXXXX.
The above example was taken for BPs, you can search for the spro settings for activities.
Hope that helps
