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.