Why is the MAPS DUL a bad idea ?
This is the Frequently Given Answer to that question.
(You can find a different approach to this answer written by Ben Bucksch. Phil Hoffman has said things on this subject as well.)
I have nothing against MAPS (and other services such as ORBZ and ORBL) in general. Indeed, I used to use ORBS myself wherever possible. (I have yet to decide which of its descendents to substitute for it.) But I think that one particular service run by MAPS, the Dial-Up List, is totally wrongheaded in its conception, and I discourage people from using it.
MAPS attempts to persuade you to use its DUL by saying that contacting an SMTP server directly, in order to deliver mail to the domain(s) that it serves by the most direct route, is "trespass".
This characterisation is complete nonsense. They are describing exactly the way that the Internet was designed to work, for goodness' sake!
Moreover, I certainly don't see how requiring all dial-up users to send their mail through an extra (totally unnecessary) hop makes it any less "trespass". If it's "trespass" when an unknown machine with a dial-up IP address contacts one's mail server to send mail to one's domain, how is it any less "trespass" when an unknown machine at some random ISP around the world contacts one's mail server to do the same thing ?
It isn't "trespass" at all. If someone from a dial-up IP address contacts your SMTP server and attempts to send mail to your domain, that is not trespass, just as pushing a letter that is addressed to you into your letterbox is not trespass. It is using Internet efficiently, and in the manner that it was designed to be used, by using the most direct route to send mail to its final destination. People who subscribe to the MAPS DUL are penalising the millions of ordinary people with dial-up accounts who want to run softwares that work the way that Internet SMTP softwares are intended to work.
MAPS also attempts to justify its DUL by saying that direct delivery
- anti-relay provisions in mail servers ...
- evidence gathering ...
- traffic limits ...
The inference that one is supposed to make is that the DUL somehow addresses these concerns. It does nothing of the sort, of course. Indeed, these concerns are entirely spurious anyway.
The idea that anti-relay provisions are "defeated" is somewhat bizarre. The whole purpose of all of the other services that MAPS provides, and of the services that other organisations such as ORBS provide, is to discourage and prevent people from using SMTP servers as third-party relays. Yet MAPS justifies its DUL by saying that it forces people to use SMTP servers as relays. This runs counter to the entire philosophy of all of the other services. Moreover, using a third party SMTP server to shoulder the burden of delivering Unsolicited Bulk Mail actually is a form of trespass. Far from preventing trespass, the MAPS DUL actually encourages it.
The notion that evidence gathering is defeated is also bizarre. What useful evidence does introducing the extra hop actually provide ? One already knows the source IP address of the originator of the mail even without the extra hop, because one's own SMTP server records that in the Received: header.
Moreover, MAPS DUL users should consider this: With direct delivery, it is your SMTP server that would be recording the originating IP address in a Received: header. However, with enforced third-party relay through the ISP's SMTP server, it is the ISP that records the originating IP address. All that your SMTP server records is the IP address of the ISP's SMTP server. Which do you trust more, your own software running on your own machines, or the software running on an ISP with whom you have no direct relationship ?
Traffic limits are also not defeated. Any sensible traffic limits will be on one's own SMTP servers. Relying on traffic limitations in the sender, which is the obvious implication that MAPS is making here, is a route to utter disaster. With traffic limits on one's own SMTP servers, incoming mail traffic from an dial-up IP address will be limited in exactly the same way as incoming mail traffic from an ISP's outgoing relay. Forcing others to use a relay SMTP server doesn't make a ha'penny worth of difference when it comes to traffic limits.
These unfounded and spurious concerns seem to be little more than scare tactics. If one actually sits down and thinks about them, their logic turns out to be full of holes, and the DUL itself really doesn't have much to do with the issues raised. One usually finds such illogical and irrelevant scare tactics being used to sell goods and services that are totally useless, and wouldn't sell at all if sold on their own merits.
Perhaps the most telling point against the MAPS DUL is that using it doesn't actually achieve the intended end. The desired end is to prevent UBM from arriving and to discourage those who would send it by making it economically unfeasible for them to do so. Forcing dial-up users to send their mail through an extra (totally unnecessary) hop does not prevent senders of UBM from sending mail. Nor does it stop it arriving at one's SMTP servers. The only people that this penalises is ISPs. Their machines end up shouldering the burden of sending the mail.
In fact, ironically, if you subscribe to the MAPS DUL you are making life easier for the people who send UBM from dial-up accounts, because it means that they can dial-up, dump a whole load of mail on their ISP relatively quickly, and hang up immediately. It's actually a good idea to encourage them to send mail directly. This allows you to implement teergrubing (a.k.a. "tarpitting") in your SMTP server, to keep the blighters on-line for as long as possible and make sure that they rack up enormous call charges. Making the initial expenditure (in terms of call costs) exceed the final gains makes it less economically worth-while for them to send UBM.