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The CDOSYS library is an implementation of the Simple Mail Transfer Protocol (SMTP) and the Network News Transfer Protocol (NNTP). CDOSYS enables applications based on the Windows XP or Windows 2000 operating system to efficiently route e-mail and USENET-style news posts across multiple platforms.

For information about CDOSYS criteria, including functional, development, security, and deployment criteria, see Collaboration Data Objects for Windows 2000 (CDOSYS).

Tool Requirements

**Windows 2000 and Windows XP:  **CDOSYS is enabled by default.

**Windows NT 4.0:  **CDO NTS must be installed from the Windows NT 4.0 SDK.


Before it sends an e-mail or bulletin board post, CDOSYS inserts two nonstandard headers into the item. This information appears anywhere before the first blank line, which marks the end of the header section and the beginning of the message body.

Depending on the type of message, CDOSYS inserts either an X-Mailer or X-Newsreader header, plus a Content-Class header, as shown in the following illustration.

CDOSYS e-mail and bulletin-board post sequencing

The following table describes the headers.

Header name Description
X-Mailer Identifies the software agent that created the e-mail message.
X-Newsreader Identifies the software agent that created the USENET-style post.
Content-Class Explains the purpose of the e-mail message or USENET-style post.


SMTP and NNTP are maintained by the Internet Engineering Task Force. For information about SMTP, see RFC 821: SIMPLE MAIL TRANSFER PROTOCOL and RFC 2821: Simple Mail Transfer Protocol. For information about NNTP, see RFC 977: Network News Transfer Protocol- A Proposed Standard for the Stream-Based Transmission of News and RFC 2980: Common NNTP Extensions.

For Microsoft licensing information, see Published Protocols and Royalty-Free License on Microsoft Developer Network (MSDN).


Port information

Uses port 25 (TCP/IP and UDP).