The operation of the mailer is quite simple. An alias is placed in the
PMDF alias file that forwards messages sent to a special mailbox name
MAILER) to the BITNET gateway channel.
BN_GATEWAY then runs as the channel master program. It
discards the PMDF envelope and the initial RFC 822 header on the
message. The message body is passed to the SMTP command interpreter for
execution. The message is deleted after it has been executed.