On Wed, Jan 21, 2004 at 01:04:31PM -0500, Meng Weng Wong wrote:
| Could ISPs please weigh in on whether your email/spam bandwidth cost is
| signicant or not, thanks.
The decision at hand is:
How important is it to reject forgeries before DATA vs after DATA at "."
time.
If it is important, that's an argument in favour of the envelope sender,
otherwise the argument allows use of headers.
From my point of view, the time cost involved in receiving a spam
I don't want that gets through my filters into my inbox, (between 3 and
30 seconds depending on whether I can reject it from the subject line
or have to open it first to manually see the content) is massive compared to
the trivial cost of the bandwidth involved in my MTA receiving the
whole thing. (I think I am well below my monthly fixed bandwidth
allocation. If so, the marginal bandwidth cost of receiving one extra
spam is, for me, zero.) If getting the data gives me a better perfomance
automated spam filter this must be worth the extra cost. I can understand
very large ISPs might see this differently, but how much is their customers'
lost time costing them in lost business ?
Another possible advantage of late automated spam detection is the
ability to set finer-grained policies for individual users at the
same domain or getting mail through the same virtual hosting MTA.
A further possible advantage is that it is possible to check
whether originating IPs have got into blacklists after the MTA
received the message, but when user logs in before opening their inbox.
Let's also look at this from the economics of the spamming operation.
If spammers have to try 10 envelope dialogues
before 1 MTA accepts data this does not impact their efficiency greatly
if they believe that all or most MTAs accepting data place these
messages into inboxes, as setting up and tearing down 10 envelope
dialogues without data costs the spammers no more than the ISPs.
However, the greater the proportion of spam which is
automatically rejected after the data stage, the greater this multiplies
the cost of the spamming operation, for which bandwidth cost is likely to
be a greater proportion of the spammers overall cost.
In practice reputable ISPs are more likely to
be concerned about overall customer satisfaction than the marginal
cost of receiving spam. This issue might put some ISPs into a kind
of prisoners dillemma, but ISPs benefit collectively, the more
spammers they can put out of business.
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