Great Circle Associates List-Managers
(March 2000)

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Subject: Re: VERPs versus batched delivery
From: John Levine <johnl @ iecc . com>
Date: Mon, 13 Mar 2000 19:19:33 -0500
To: "Bernie Cosell" <bernie @ fantasyfarm . com>, list-managers @ GreatCircle . COM
In-reply-to: <38CC9B41.5272.3CE2056@localhost>
References: <>

>The last two are OK, but I'm not convinced about the first two: in
>'normal' delivery, there's just *one* copy of the message and it gets
>routed all over hell and gone... is the CPU to make and manage all those
>extra copies trivial?  even if trivial, how does it end up being
>_reduced_ utilization.

Pragmatically, qmail does single deliveries with VERP, and it's a lot faster
than sendmail. I don't know how much is the simpler design due to single
deliveries, and how much is not having decades of historical cruft glommed
into one giant program, but it hardly matters in practice.

| That is, it strikes me as the difference, in usenet terms, between
>multiple-newsgroup-posting and crossposting,

Not really. The crucial difference is that it's useful to customize e-mail
to individual recipients. VERP puts a custom envelope return address on each
recipient's message, which permits almost completely automated bounce
handling. This does work, I've used it for ages on lists I run, and it
avoids vast amounts of manual effort on the part of the list admin.

Once you send separate copies per recipient, you can also usefully customize
the message body. In the tag at the bottoms of the message, you can put the
address to which it was sent, useful to track down bounces from systems that
bounce back messages while removing all trace of the original envelope. You
can also add "To unsubscribe, send a message to
<>" (substituting
the actual address for user and so that users, even whose
addresses have changed since they subscribed, can easily get off the list.

Dan Bernstein has pointed out in his usual annoying but accurate way that
SMTP wasn't designed to be particularly efficient in bandwidth usage, and if
that's what you're worried about, there are a lot of ways other than
multiple deliveries to reduce bandwidth. The most effective is sublists like
LISTSERV uses -- distribute the list database to hosts close to the
recipients, then send one copy with one address from the master host to the
subhosts that then redeliver.

John Levine,, Primary Perpetrator of "The Internet for Dummies",
Information Superhighwayman wanna-be,, Sewer Commissioner
Finger for PGP key, f'print = 3A 5B D0 3F D9 A0 6A A4  2D AC 1E 9E A6 36 A3 47

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