"Scott D. Yelich" <[EMAIL PROTECTED]> wrote:
>
>Wha? Why so? Sendmail supresses dup addresses before sending. It's a
>very nice feature.
This is because sendmail is monolithic and qmail is modular(*).
Sendmail can suppress *some* duplicates by expanding lists before
sending the message. With qmail, the parts that route messages and
handle lists are at the opposite end of the process: qmails-send does
the routing, and qmail-local does the lists. For qmail to suppress
duplicates like sendmail, qmail-send would have to know where the
message will end up being delivered by qmail-local, preempt the normal
delivery, and send the message only to the unique recipients.
In reality, though, MTA-based duplicate elimination is imperfect. For
one thing, it can only suppress duplicates that originate on one
system. If a message is sent to list1@host1 and list2@host2, and
[EMAIL PROTECTED] is on both list1 and list2, no MTA can possibly
prevent duplicate delivery. Even sendmail's duplicate suppression is
flawed. It can only suppress duplicates that come from direct alias
expansion. If another delivery step is required, as with Majordomo
lists that use "resend" to implement moderation, duplicates will still
result.
Some people, myself included, think MTA duplicate suppression is a bad
idea. If a message is sent to a person N times, the person should get
N copies. Period. If the user doesn't want to see duplicate messages,
that's an issue best dealt with by his MUA(s).
-Dave
*See <URL:http://Web.InfoAve.Net/~dsill/lwq.html#Modular system architecture>
