Relationship between 1.x CDO Libraries and CDOSYS.DLL

This article discusses how Microsoft Collaboration Data Objects (CDO) for Windows 2000 (CDOSYS) relates to earlier versions of CDO (1.x) as well as Collaboration Data Objects for NT Server (CDONTS).

CDOSYS and CDONTS (1.x) are both object libraries designed to enable SMTP Messaging. However, while CDOSYS provides all of the same functionality as CDONTS (plus substantially more), the two are not code-compatible. Also, because CDOSYS is based on the SMTP and NNTP standards, it does not directly support mailboxes and is not code- compatible with CDO (1.1, 1.2, 1.21).

Because CDOSYS is not a direct replacement for CDONTS (1.x) nor a replacement for CDO (1.x), they can be used on the same system concurrently, if required. If a program or script needs to work with messaging objects using Microsoft Exchange Server as well as the SMTP and NNTP protocols, it can simultaneously access the CDO (1.1, 1.2, 1.21) Library, the CDO (1.1, 1.2, 1.21) Rendering Library version, the CDONTS (1.x) Library, and the CDO for Windows 2000 (CDOSYS) Library. An application running on an Automation controller such as Visual Basic can call all these libraries and coordinate their activities.

The most notable differences between CDONTS (1.x) and CDOSYS is that CDOSYS:

• Provides great support for MIME messages.
• Can be run on the client side.
• Supports selection among multiple SMTP configurations
• Supports server events

CDOSYS requires Windows 2000 and either a local or remote SMTP Server (which can be an Exchange server).

For more information about the differences listed above or about CDO for Windows 2000 (CDOSYS) in general, see the "CDO for Windows 2000" topic in the Microsoft Developer Network (MSDN) Library (January 2000 or later) and related articles in the Microsoft Knowledge Base.