silentetrn keywords control PMDF's response when a sending
SMTP client issues the SMTP ETRN command, requesting that PMDF attempt
to deliver messages in the PMDF queues.
that PMDF will attempt to honor all ETRN commands and will echo back
the name of the channel that will be run in response to the ETRN
silentetrn tells PMDF to honor all ETRN commands,
but without echoing back the name of the channel which the domain
matched and which PMDF will hence be attempting to run.
domainetrn tells PMDF to honor only those ETRN commands
that specify a domain with an @; it also causes PMDF not to echo back
the name of the channel which the domain matched and which PMDF will
hence be attempting to run.
disableetrn disables support
for the ETRN command entirely; ETRN will not be advertised by the SMTP
server as a supported command. The default behavior, if none of these
keywords is explicitly specified, corresponds most closely to
blocketrn tells PMDF not to honor an ETRN command if the
ETRN command attempts to run that channel. Note that this keyword is
therefore relevant on a destination channel, not on the incoming TCP/IP
channel (unless that incoming channel would also be the destination
channel for an attempted ETRN command).
See also Section 188.8.131.52 for a discussion of the ALLOW_ETRNS_PER_SESSION channel option, which may be used to limit the number of ETRN commands which PMDF will honor during a single session.