SMTP rate-limits [Was: Re: ingress SMTP]

["Paul Ferguson" <fergdawg () netzero net>]

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- -- Simon Waters <simonw () zynet net> wrote:

> If the ISP blocks port 25, then the ISP is taking responsibility for 
delivering all email sent by a user, and they have to start applying rate 
limits. Otherwise if they send all email from their users, all they've done
is take the spam, and mix it in with the legitimate email, making spam 
filtering harder.
>

Okay, I can understand why an ISP might want to apply SMTP
rate-limits, but to clarify, I'm assuming you meant that ISPs
(if they do block tcp/25 outbound to anything other than their
own MTAs) need to watch for excessive SMTP utilization, which might
indicate a spammer-client (?).

...as opposed to arbitrary SMTP rate-limits.

Yes?

- - ferg

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--
"Fergie", a.k.a. Paul Ferguson
 Engineering Architecture for the Internet
 fergdawg(at)netzero.net
 ferg's tech blog: http://fergdawg.blogspot.com/