4.40.5: IPBlock 451 versus 550

David Lee t.d.lee at DURHAM.AC.UK
Thu Mar 17 15:05:46 GMT 2005

On Wed, 16 Mar 2005, Julian Field wrote:

> David Lee wrote:
>> [...]
>> The idea seems to be to return a 4xx-like failure to connections from
>> hitherto new/unknown places, and notes that the connection attempt has
>> been made ("if I haven't met you before, then 4xx.").  A large proportion
>> of spam engines simply won't bother to retry.
>> By contrast, legitimate email (yes, and some residual spam) would always
>> try again a few minutes later, and so when it does, this time the call is
>> accepted ("I've just met you, so I accept you 200-like").
>> [...]
> Very interesting idea. I will have a think. Unfortunately I would have
> to accept the first mail in order for it to get into MailScanner at all.
> And that may defeat the idea altogether. Any thoughts?

Of course.  (Hits self over the head with clue-stick.)  And thanks to a
couple of other folk who also kindly showed me the obvious (and to yet
others who showed that it might have bad side-effects on some perfectly
legitimate sending ISPs).


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:                                           University of Durham  :
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