Filtering on List-Id (was Re: Administrivia: Subject line tagging)

[Derek Martin]

On Sun, Apr 18, 2004 at 09:11:09PM -0400, bscott at ntisys.com wrote:
>   But anyway, the "List-Id" header is guaranteed to be present and the same
> for all messages delivered through this mailing list.  So, one should filter
> on that, and not anything else, to identify list mail.

This is a point worth taking note of.  Filtering ONLY on list-id  can
fail.  Often, a poster replies to both the list, and the original
poster.  In this case, the OP will normally receive two copies of the
message: one from the list management software (with the expected
List-Id header), and one which comes directly from the sender (which
will NOT have the List-Id header).

If you DON'T  use procmail (or something else) to filter duplicate
messages, you'll get two copies of the message.  One will be
"properly" filtered, and the other will not.  If you DO use procmail
to filter duplicates, you will only receive one copy of the message.
You probably will first receive the message which comes directly from
the sender, and thus it will not be filtered properly.

This is the rule I use to filter all mail from the GNHLUG and BLU
mailing lists into my "Linux" folder.  It's not 100% perfect, but it
fails (with false positives) only in extremely rare cases.

  :0 
  * (gnhlug|discuss).*@.*(gnhlug|blu)
  folders/Linux

This matches on any header, any occurrence of the following:

  gnhlug-discuss at mail.gnhlug.org
  discuss at gnhlug.org
  discuss at blu.org

...as well as a number of patters which are not official list
addresses for either list, but which are very unlikely to occur
anywhere else.

Of course, if you're filtering only for gnhlug, you could pretty much
eliminate false positives with this:

  * gnhlug-discuss at mail\.gnhlug\.org|discuss at gnhlug\.org

I will also note for the record that the List-ID header for this list
appears to have a small error...  I think there's a '.' where the '@'
should be.  It may not be crucial, but if people expect to match on
'gnhlug-discuss at mail.gnhlug.org', it will fail.

-- 
Derek D. Martin    http://www.pizzashack.org/   GPG Key ID: 0xDFBEAD02
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