SCO UNIX System V/386 Release 3.2 Operating System Version 4.2 

          I wish to configure MMDF so as to prevent other organizations' mail
          from being routed via my system, for example:

            Z.fu.com       X.bar.com
                ^               ^
                |               |
                v               v
                 "A.internal.com"
                  (Mail Gateway)
                        ^
                        |
                        v
                "B.internal.com",
                "C.internal.com",
                      ...

          I want to allow my systems to both send and receive mail from
          external systems (such as Z.fu.com or X.bar.com), but prevent
          external systems from routing mail to each other via my gateway
          (such as Z.fu.com to X.fu.com via A.internal.com).

          MMDF has the facility to apply authorization for channels on a
          per-host basis.

          (1) Add the following entry to define an authorization file in
          /usr/mmdf/mmdftailor:

                MTBL name=authhosts, file="authhosts",
                show="MMDF host/channel authorization"

          (2) Edit the MCHN entry for the channel(s) used to communicate
          with systems external to internal.com and add the entries:

                auth=inblock, outsrc=authhosts, indest=authhosts

          This specifies that only hosts and channels listed in:

                /usr/mmdf/table/authhosts

          should be allowed to route mail in via this channel.  Note that the
          change to the MCHN entry must appear in the file after the MTBL entry,
          or there may be errors from dbmbuild(ADM).

          (3) Edit /usr/mmdf/table/authhosts and add an entry:

                local:

	  to allow mail originating on the local channel (that is, from
	  A.internal.com) to be sent out over this channel and to allow mail
	  received via this channel to be delivered to the local channel (to a
          user on A.internal.com).

          (4) Add an entry for every system that is allowed to send
          mail out via this channel or that shoudl be allowed to receive mail
          via this channel:

                B.internal.com:
                C.internal.com:

          (5) Rebuild the MMDF database using dbmbuild(ADM) and
          restart the deliver(ADM) daemons.

          An example entry is shown below:

                /usr/mmdf/mmdftailor
...
...
...
MTBL name=authhosts,    file="authhosts",       show="MMDF authorization"

MTBL    smtpchn,        flags=ns,       show="DNS fully qualified domains",
        flags=channel

MCHN    smtp, show="SMTP Delivery", ap=822, tbl=smtpchn, mod=reg,
        auth=inblock, outsrc=authhosts, indest=authhosts
...
...
...

                /usr/mmdf/table/authhosts
local:
A.internal.com:
B.internal.com:
C.internal.com: