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Annotation of 43BSDReno/share/doc/ucs/mmdf/p7, revision 1.1

1.1     ! root        1: .SH
        !             2: The List Channel
        !             3: .PP
        !             4: The list channel was developed as the result of BRL's experience
        !             5: in managing \fBlarge\fR Internet mailing lists.
        !             6: Two major problems were discovered with dealing with mailing lists
        !             7: in MMDFI.  First, since \fBsubmit\fR always verifies all known addresses
        !             8: for a message at submission time, if you were on the machine with
        !             9: a large list and submitted mail to the list you would have to wait
        !            10: for every address on that list to be verified.
        !            11: On a busy machine
        !            12: with a list of hundreds of addresses, this could take
        !            13: five or ten minutes.
        !            14: Annoying as this may be for people,
        !            15: the situation was worse for mail submitted over communications
        !            16: channels like TCP/IP.  The remote end would continually time out
        !            17: before the message had been completely verified so the message
        !            18: could never be sent.
        !            19: .PP
        !            20: The second problem with large lists was that there were always
        !            21: rejected mail notices going back to those
        !            22: least able to do anything about the mail problem, the original
        !            23: sender of the message.  What was really desired was a method to
        !            24: try to have returned mail go to the list maintainer instead
        !            25: of the message's original sender.
        !            26: .PP
        !            27: The solution to both of the problems is embodied in the list channel.
        !            28: This is a channel with an incestuous relationship
        !            29: to \fBsubmit\fR, \fBdeliver\fR,
        !            30: and the alias file.
        !            31: Use of the list channel is best described in parallel with the
        !            32: special entries for the list channel in the alias file.
        !            33: If we were maintaining a large list called ``biglist'', the following
        !            34: entries would be in the alias file:
        !            35: .nf
        !            36: .ta 2.6i
        !            37: .sp .5
        !            38: .in +.6i
        !            39: biglist:       biglist-outbound@list-processor
        !            40: .br
        !            41: biglist-outbound:      </usr/mmdf/lists/biglist-file
        !            42: .br
        !            43: biglist-request:       maintainer
        !            44: .in -.6i
        !            45: .fi
        !            46: .sp .5
        !            47: The pseudo-host ``list-processor'' has its own domain table and its
        !            48: own host table but represents no actual host.  If someone submits
        !            49: mail to biglist, \fBsubmit\fR will find the alias entry and
        !            50: upon finding that it's
        !            51: not a local address, will queue it to the host ``list-processor'',
        !            52: so verification is complete after only one lookup.
        !            53: Unknown to
        !            54: \fBdeliver\fR, the list channel simply calls \fBsubmit\fR and feeds it the
        !            55: aliased addresses, ``biglist-outbound''.
        !            56: This time the actual verification is done on the contents of
        !            57: the address list ``biglist-file''.  Since the list channel is processed
        !            58: by a background daemon, no one is forced to wait through the
        !            59: verification process except the background daemon itself, which doesn't care
        !            60: how long it takes so long as it completes.
        !            61: .PP
        !            62: The list channel also performs another function to try to
        !            63: eliminate the problem of failed mail messages.
        !            64: For each address given to it, (normally just one), the list channel
        !            65: sees if there is a matching ``\fIlistname\fR-request'' entry in the alias
        !            66: table.  It knows enough to try stripping any ``\-outbound''s from
        !            67: the name first though.  If a ``\-request'' entry is found, then
        !            68: that address is substituted instead of the original return
        !            69: address.  The message text is \fInot\fR altered, but the new return address
        !            70: is recorded for use when resending the message.
        !            71: The new return address
        !            72: is supplied in SMTP ``MAIL FROM:<\fIaddress\fR>'' commands and any other
        !            73: situations where the return address is directly specifiable.
        !            74: .PP
        !            75: The changing of the return address is useful only if mail is rejected
        !            76: when submitted to the foreign host or if that host is smart enough to keep
        !            77: the return address information around.  Many hosts do not maintain this
        !            78: information,
        !            79: and many of the same hosts are also problematic in that they
        !            80: will completely accept a message containing total garbage and
        !            81: decide to tell you about it later.  This is precisely what MMDF tries
        !            82: to avoid by submission-time verification.

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