Collaboration Data Objects

Originally known as Active Messaging, the Collaboration Data Objects (CDO) library allows you to access the Global Address List and other server objects, in addition to the contents of mailboxes and public folders. It is used for some key Outlook programming tasks, such as displaying an address book for the user to pick from. However, with the advent of the Outlook Email Security Update, CDO is far less useful, and many developers are using Redemption instead in order to avoid the security prompts.

Outlook 2007 adds objects and methods to move a long way toward parity with CDO -- without security prompts. For example, the PropertyAccessor and StorageItem objects provide access to hidden fields and messages.

CDOLive is the premier resource site for Collaboration Data Objects, with samples, articles, lists of undocumented MAPI properties, and a discussion forum.

CDO 1.21 is not officially supported in a .NET Framework environment, although we've seen people use it. See Support Policy for Microsoft Exchange APIs with .NET Framework Applications and FYI: Why are MAPI and CDO 1.21 not supported in managed (.NET) code?.

Documentation

• CDO 1.21 documentation  
• CDO Help File (also on Exchange Server CD)
• CDO 1.21 Library -- Chapter 2 from Professional CDO Programming

Articles

• Digging Deeper into CDO (CDOLive)
• Introduction to Collaboration Data Objects
• CDO Part I

Top CDO techniques for Outlook applications

• To pop up the Select Names dialog and work with selected names
• To get the sender's address from a mail message
• AddHeader3 Form -- Sample Outlook form to demonstrate how can you add an X-header in your outgoing Internet messages using CDO 
• Use CDO To Walk Through The Exchange Mail Store -- Uses CDO to access Outlook contact item properties

More techniques for client-related applications

• Digging deeper into CDO, Property Tags and Types (CDOLive) -- How to access Outlook properties
• HOWTO: Access MAPI Address Books with Active Messaging 1.1
• DLL to Read and Write RTF with Active Messaging
• Outlook Custom Categories Form -- Uses a hidden CDO message to hold the categories for a folder; very handy technique for any type of folder-specific list. (CDOLive)
• HOWTO Access SMTP Headers of a Message Using CDO (1.x)  -- Also see the code samples at http://victori.hypermart.net/
• HOWTO Work with Distribution Lists Using CDO (1.x) from Visual Basic -- for the Personal Address Book only
• HOWTO Extract MAPI Properties of Current User in Outlook Form
• HOWTO Force a Particular Internet Encoding by Using MAPI
• You cannot rename default folders by using the Outlook 2003 object model -- but you can with CDO

Discussion

• Ask the Experts at CDOLive
• microsoft.public.exchange.applications newsgroup at msnews.microsoft.com

Problems

If you plan to install Outlook 2003 on client machines, you will probably need to update the version of CDO running on your server first. In Exchange 2000 and 2003, you may have server-based applications that use CDO for data access. Once you use Outlook 2003 against an Exchange mailbox, a change takes place in the mailbox properties that is incompatible with CDO. Exchange 2000 or 2003 applications that use CDO to access the mailbox may fail completely if they call the PR_FREEBUSY_ENTRYIDS MAPI property. You can contact Microsoft Product Support Services to obtain a hotfix for your version of Exchange:

• Exchange 2003
• Exchange 2000

Notes

Some confusion exists over other libraries with "CDO" in their name -- CDONTS, CDO for Windows 2000, and CDO for Exchange (2000/2003). The first two can be used for creating and sending messages, but otherwise have little client application in an Outlook programming environment. See:

• CDOLive - Digging deeper into CDO, History & Future
• Collaboration Data Objects Roadmap for Windows 2000 and Exchange 2000 -- different versions of CDO, but as noted above, not the same as the one in Outlook