Laird Breyer wrote:
For example, consider a high volume mailing list (Arnt's bugtracking
mailing list example). A non-list member X makes a post, but has no
intention of monitoring the mailing list, or even to subscribe to it
and keep it in a separate folder to see if somebody responds. He
doesn't know how quickly a response might come, a few hours, a few
weeks, or whether a response will come at all. Having better threading
or filtering is useless, because the mailing list traffic is not going
to be monitored by his MUA.
But the mailing list server knows immediately that X is not a list
member, so if his post is accepted (this is a policy issue), then if
somebody else responds to this post on the mailing list, the list
server can send X a copy of the message. The people who are list members
don't need to know if X is a list member or not, everything is handled
by the list server.
Whether you realize it or not you're making quite a few assumptions
which you haven't mentioned:
1. That mailing list software is designed to keep track of every
message sent to the list, and to examine every such message for
possible relationships to other messages. Even were that always
feasible (see next assumption), it is likely to be impractical
especially in the situations where you apparently believe it
would be most useful ("For example, consider a high volume
mailing list"). As the number of messages increases, the number
of comparisons increases quadratically, and the complexity of
each comparison may also increase rapidly (see below).
2. That it is always possible to establish relationships between
messages (Message-ID, In-Reply-To, and References fields are
optional).
3. That it is possible to accurately determine whether a sender is
a list member (avoiding forgeries where e.g. a spammer forges
either a message header address field or the envelope sender
address, while accurately recognizing messages sent by a list
member from an alternate account, via a public wireless access
point, via a web mail interface, etc.).
4. That every person who submits a message to a mailing list
wishes to receive one or more email responses (that is untrue
for some people who monitor list activity via a web archive
of the list, whether or not they are registered as being "on"
the list).
You also haven't indicated whether you think that a response to
a response to a message sent by the hypothetical X should also
be mailed to X.