Definitions of Verbs That Are Used Between 2 Exchange Servers

This article lists definitions of 3 verbs that Exchange uses for communication. As of February 2003, these 3 verbs, (XEXCH50, X-LINK2STATE, and X-EXPS) are not fully defined in Exchange documentation. You may need these definitions when you configure Exchange or network filters. For example, you may have to add these verbs to the Exchange routing tables to make it possible for 2 Exchange servers to communicate through a firewall.

Definitions of XEXCH50, X-LINK2STATE, and X-EXPS

• X-EXPS
  X-EXPS is a verb that is proprietary to Exchange, though it is similar to AUTH. There is no maximum size limit for the data chunks, or the number of data chunks exchanged. The syntax of the data commands and responses depends on the AUTH package that you select, such as LOGIN, NTLM, GSSAPI, or others. For more information, see the AUTH RFC.
• X-LINK2STATE
  X-LINK2STATE commands and responses are specific extensions of SMTP. This command is proprietary to Exchange, and is designed to exchange routing topology information between Exchange SMTP servers. The maximum possible size of any X-LINK2STATE command and response is 1,024 bytes. This size is frequently the actual size of X-LINK2STATE commands and responses.
• XEXCH50
  XEXCH50 is the Exchange extension SMTP that is used to relay certain message properties such as envelope message and recipient properties. The XEXCH50 command is not longer than 50 bytes, and the longest XEXCH50 response is no longer than 40 bytes. An XEXCH50 command that has received a success type response is then followed by a binary data chunk. The size of this data chunk corresponds to the first argument of the XEXCH50 command. Data chunks cannot be greater than 1 gigabyte (GB). With successful data transmission, a success response is no longer than 20 bytes. If any errors occur, the data chunk is not longer than 40 bytes.
  
  XEXCH50 command, response <= 50 bytes
  XEXCH50 data chunk <= 1 GB
  XEXCh50 data response <= 40 bytes

For additional information about routing using Exchange 2000 Server, click the following article numbers to view the articles in the Microsoft Knowledge Base: