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From: L-Soft list server at SecurityFocus.com (1.8d) (LISTSERV@LISTS.SECURITYFOCUS.COM)
Date: Mon Apr 16 2001 - 07:01:19 CDT

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    Mon, 16 Apr 2001 06:01:19

    This message is a "probe" for your subscription to the CISSPSTUDY list.
    You do not need to take any action to remain subscribed to the list, and
    in particular you should not reply to this message. Simply discard it
    now, or read on if you would like to know more about how this probing
    mechanism works.

    A "probe" is a message like the one you are reading, sent to an
    individual subscriber and tagged with a special signature to uniquely
    identify this particular subscriber (you can probably not see the
    signature because it is in the mail headers). If the subscriber's e-mail
    address is no longer valid, the message will be returned to LISTSERV and
    the faulty address will be removed from the list. If the subscriber's
    address is still valid, the message will not bounce and the user will not
    be deleted.

    The main advantage of this technique is that it can be fully automated;
    the list owner does not need to read a single delivery error. For a large
    or active list, the manpower savings can be tremendous. In fact, some
    lists are so large that it is virtually impossible to process delivery
    errors manually. Another advantage is that the special, unique signatures
    make it possible to accurately process delivery errors that are otherwise
    unintelligible, even to an experienced technical person.

    The drawback, however, is that this method lacks flexibility and
    forgiveness. Since the Internet does not provide a reliable mechanism for
    probing an e-mail address without actually delivering a message to the
    human recipient, the subscribers need to be inconvenienced with yet
    another "junk message." And, unlike a human list owner, LISTSERV follows
    a number of simple rules in determining when and whether to terminate a
    subscription. In particular, a common problem with automatic probes is
    mail gateways that return a delivery error, but do deliver the message
    anyway. LISTSERV has no way to know that the message was in fact
    delivered, and in most cases the subscriber is not aware of the existence
    of these "false" error reports. If this happens to you, LISTSERV will
    send you another message with a copy of the delivery error returned by
    your mail system, so that you can show it to your technical people.