When a PMDF server accepts an incoming connection from a remote system it must choose a channel with which to associate the connection. Normally this decision is based on the transport used; for example, an incoming TCP/IP connection is automatically associated with the tcp_local channel.
This convention breaks down, however, when multiple outgoing channels with different characteristics are used to handle different systems over the same transport. When this is done incoming connections are not associated with the same channel as outgoing connections, and the result is that the corresponding channel characteristics are not associated with the remote system.
switchchannel keyword provides a way to eliminate this
switchchannel is specified on the initial
channel the server uses, the IP address of the connecting (originating)
host will be matched against the channel table and if it matches the
source channel will change accordingly. If no IP address match is found
or if a match is found that matches the original default incoming
channel, PMDF may optionally try matching using the host name found by
doing a DNS reverse lookup; see Section 126.96.36.199. The source channel may
change to any channel marked
allowswitchchannel (the default).
noswitchchannel specifies that no channel switching should
be done to or from the channel.
switchchannel on anything other than a
channel that a server associates with by default will have no effect.
switchchannel only affects SMTP channels, but
there are actually no other channels where
would be reasonable. In particular, PhoneNet channels never need to
switch since they are inherently point-to-point.