Compliant spammers (II)

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There's been a lot of traffic on NANOG about CNET's report about spammers sending to port 25 on the ISP mail server (start here). The consensus seems to be that this is old stuff and CNET just noticed:
From: Suresh Ramasubramanian
Date: Thu Feb 03 07:13:18 2005

On Thu, 3 Feb 2005 11:42:55 +0000,
> that botnets are now routing their mail traffic through the local
> ISP's mail servers rather than trying their own port 25
> connections.

Now?  We (and AOL, and some other large networks) have been seeing
this thing go on since over a year.

> Do you let your customers send an unlimited number of
> emails per day? Per hour? Per minute? If so, then why?

Doing that - especially now when this article has hit the popular
press and there's going to be lots more people doing the same thing -
is going to be equivalent of hanging out a "block my email" sign.

One additional thing that I think wasnt mentioned in the article -
Make sure your MXs (inbound servers) are separate from your outbound
machines, and that the MX servers dont relay email for your dynamic IP
netblock. Some other trojans do stuff like getting the ppp domain name
/ rDNS name of the assigned IP etc and then "nslookup -q=mx", then set itself up so that all its payloads get delivered
out of the domain's MX servers

This kind of stuff is just really hard to stop.

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Old trick it may be, but it's about to become a LOT more prevalent; as Brian McWilliams reports at , Send-Safe (the biggest spamware tool) has just added support for it.

(I didn't post this on NANOG, because it's off-charter there btw. Unfortunately, NANOG isn't a great place to pick up reliable spam-related info as a result.)

Thanks. Can you suggest a good mailing list for spam info?

Goodman & Rounthwaite had a good paper in EC on mechanisms for stopping outgoing spam on the ISP side, focusing on the incentives of the spammers. (They focus especially on email service providers that provide free e-mail.)

They show that limiting message on a time basis is unlikely to work: spammers usually get to send about 1000 messages before their account is terminated as spam, so this just makes them get there more slowly or set up accounts in parallel rather than in series. Their solution is to provide a cost (computational challenges or HIPs) for the first, say, 100 messages, and then never again. This works about as well as imposing the cost forever because spammers (but not legitimate users) get caught after 1000 messages.

It's a bit off-topic, but pretty interesting.

Paper here:

the good antispam mailing lists I know of are Spam-L: and spam-research: .

The latter seems quite useful, I've just come across it recently, but the members are clueful and volume low. Spam-L has a few vocal members, so a pinch of salt may be necessary; but there's clueful people there too.

The ASRG list and IETF lists are to be avoided; they're a wingnut-magnet.

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