To access the one-off table belonging to one of your containers, MAPI calls the container's IMAPIProp::OpenProperty method to open the PR_CREATE_TEMPLATES property with the IMAPITable interface. Your container is asked to return its one-off table when a client application is trying to add a recipient to the container. If the container allows any recipients, your provider can either return its own table implementation or call IMAPISupport::GetOneOffTable to return the MAPI implementation.
The set of templates in the container one-off table should reflect the type of recipients that the particular container can hold. Typically, this includes one or two templates, templates for creating an individual messaging user or a distribution list. The entry identifiers for these templates are held in the PR_DEF_CREATE_MAILUSER and PR_DEF_CREATE_DL properties. However, containers are by no means limited to these types of entries. They can hold other types of recipients or non-recipient entries such as directories.