The End-To-End Internet (was Re: Blocking MX query)

Sean Harlow sean at
Tue Sep 4 19:21:25 UTC 2012

On Sep 4, 2012, at 14:22, Jay Ashworth wrote:

> I find these conflicting reports very conflicting.  Either the end-to-end
> principle *is* the Prime Directive... or it is *not*.

Just because something is of extremely high importance does not mean it still can't be overridden when there's good enough reason.

In this case, in the majority of "random computer on the internet" IP blocks the ratio of spambots to legitimate mail senders is so far off balance that a whitelisting approach to allowing outbound port 25 traffic is not unreasonable.  Unlike the bad kinds of NAT, this doesn't also indiscriminately block thousands of other uses, it exclusively affects email traffic in a way which is trivial for the legitimate user to work around while stopping the random infected hosts in their tracks.

Many providers also block traffic on ports like 137 (NetBIOS) on "consumer" space for similar reasons, the malicious or unwanted uses vastly outweigh the legitimate ones.

The reason bad NATs get dumped on is because there are better solutions both known and available on the market.  If you have an idea for a way to allow your laptop to send messages directly while still stopping or minimizing the ability of the thousands of zombies sharing an ISP with you from doing the same the world would love to hear it.
Sean Harlow
sean at

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