Girish Kulkarni skrev:
On Wed, 30 Sep 2009, Ric Otte wrote:
I believe it is bad to use procmail to reject mail, ...
Why is that?
You got a link with a good technical explanation in another reply. The
importance of that info may not be apparent if you are not familiar with
how email works. Let me try an analogy. Imagine email is just like
regular mail exept that everything is delivered by the sender in person
to a local post-office, which runs a truck with the mail to the
recipient's local post-office. All recipients pick up their mail at
their local post-office. A mail-server is a post-office. Every time mail
enters a post-office, it puts a "Received" line on the envelope, latest
at the top.
Say you go pick up all your mail and bring it home to sort at the
kitchen-table. The kitchen-table is procmail. You find junk-mail in the
pile on your kitchen-table and label it "return to sender" and bring it
back to the post-office. On the internet all junk-mail in practice has
forged sender address, so some innocent soul will get his mail-box
filled with "returns" that are actually not from him. The better way to
deal with junk-mail is to have your local post-office simply refuse any
mail from dubious commercial mass-mailers. That way innocent by-standers
are protected, and resources taken by bringing the junk all the way to
your kitchen-table are saved. If the mail was in fact not junk, the real
sender will be notified by his own local post-office of the failure,
because local post-offices will usually notify local customers when
their truck was unable to deliver. The recipient's post-office can in
some cases even inspect the contens of the mail WHILE THE DELIVERY VAN
IS WAITING and say "No thanks". This is the stage of delivery postfix
calls "Before-queue", and you want to reject as much as possible at this
stage, before the mail is put into your P.O.Box. Postfix can also mark
mail to be filtered, in effect have a clerk go over the mail that is to
be put into your P.O.Box after the delivery truck has left. At this
stage postfix can bounce stuff back to the sender (REJECT action), but
usually it is not advisable to do so. Just let postfix "drop it on the
floor" (DISCARD action). I imagine exim has similar options.
P.S: One effective way to send out loads of spam, is to send it to
non-existant adresses hosted on innocent, but misconfigured,
mail-servers. This misguided, old-fashioned post-office will then
proceed to deliver the entire mail "back" to the "sender" in its own
misguided mind, while it actually is helping spread spam by using its
good name and delivery system to deliver the spam mail to a third party.
In this day and age incompetence is actually just another name for evil,
and such old-timers will be summarliy put into a lot of RBL-lists.
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