CDO Object Hierarchy

Session
    AddressLists collection
        AddressList
            Fields collection
                Field
            AddressEntries collection
                AddressEntry
                    Fields collection
                        Field
                AddressEntryFilter
                    Fields collection
                        Field
   Folder (Inbox or Outbox)
        Fields collection
            Field
        Folders collection
            Folder
    InfoStores collection
        InfoStore
            Fields collection
                Field
            Folder
 

Folder object has the following sub hierarchy:

Folder
    Fields collection
        Field
    [Folders collection... Folder...]
    Messages collection
        AppointmentItem
            RecurrencePattern
        GroupHeader
        MeetingItem
        Message
            Attachments collection
                Attachment
                    Fields collection
                        Field
            Fields collection
                Field
            Recipients collection
                Recipient
                    AddressEntry
                        Fields collection
                            Field
        MessageFilter
            Fields collection
                Field

And this is a brief description of each object:

AddressEntries - collection of address entries.
AddressEntry - one address.
AddressEntryFilter - criteria to restrict search on collection of address entries.
AddressList - container for collections of address entries.
AddressLists - collection of address lists.
AppointmentItem - represents an appointment.
Attachment - represents an attachment to a message.
Attachments - collection of attachments.
Field - represents one MAPI property.
Fields - collection of fields.
Folder - a container that contains subfolders and messages.
Folders - collection of folders.
GroupHeader - represents a header for grouping messages in tables.
InfoStore - information store.
InfoStores - collection of information stores.
MeetingItem - represents a meeting.
Message - an individual item (such as a mail message) in a folder.
MessageFilter - criteria to restrict search on collection of messages.
Messages - collection of messages.
Recipient - represents a recipient.
Recipients - collection of recipients.
RecurrencePattern - describes recurrence pattern for appointment items.
Session - one and only top level object.