Relationship between CDOSYS & CDOEX

CDOEX is a superset of CDOSYS; this means that CDOEX contains all of the functionality of CDOSYS, plus additional functionality for use with Microsoft Exchange Server 2000. When CDOEX is installed on a computer, it takes over the functionality that was previously provided by CDOSYS. Any program that makes calls to CDOSYS will now call CDOEX instead.

When CDOEX is installed (by installing Microsoft Exchange Server 2000, Microsoft Office XP, or other programs), the CDO for Windows 2000 reference is removed from the list of possible references available to Visual Basic applications. However, the CDO for Exchange 2000 library is available, and developers can use CDOEX just as they would have used CDOSYS.

This relationship can affect the development of Visual Basic projects, including programs developed with Microsoft Visual Basic for Applications (VBA) or Visual Basic Scripting Edition (VBScript) in the following way:

  • Programs created using CDOSYS will function without change on computers with CDOEX installed.
  • Applications created using CDOEX and using only the objects associated with CDOSYS (CDO.Message for instance), will also function as expected on computers with only CDOSYS installed.
  • The full CDOEX object model is designed for use on computers with Microsoft Exchange 2000 Server installed. Code developed for CDOEX using CDOEX-specific objects will NOT execute correctly on computers without Exchange 2000 Server installed.

Note CDOSYS and CDOEX are not direct replacements for CDO 1.21 (CDO.DLL); their presence has no effect on the CDO 1.21 library.

For more information about CDO libraries, click the following article numbers to view the articles in the Microsoft Knowledge Base:

Relationship between 1.x CDO Libraries and CDOSYS.DLL

Where to acquire the CDO Libraries (all versions)

Skip to main content