TCP/IP channel option files control various characteristics of TCP/IP channels. Channel option files must be stored in the MTA configuration directory and named x_option, where x is the name of the channel. For example, /msg-svr-base/config/tcp_local_option
The option file consists of one or more keywords and associated values. For example you can disable mailing list expansion on your server by including the DISABLE_EXPAND keyword in the option file and setting the value to 1.
Other option file keywords allow you to:
SMTP channel options that take effect after channel switching should be placed in the appropriate channel option file (that is, tcp_local_option, tcp_auth_option, tcp_intranet_option). SMTP channel option files that take effect before channel switching MUST be placed in the channel option file for the original channel—usually tcp_local, because messages usually enter the MTA via the tcp_local channel before channel switching occurs.
For information about all channel option keywords and syntax, see the Sun Java System Messaging Server 6.3 Administration Reference.