Auteur: normallybaffled Datum: Aan: exim-users Onderwerp: Re: [exim] Blocking Authenticated Exim user whose ip address is in
an RBL
W B Hacker wrote: >
> normallybaffled wrote:
>>
>>
>> You shoudl ordinarily expect that travelers, WiFi users, adsl, dsl,
>> residantial
>> dial-up WILL be on IP-blocks not intended for MTA use AND that fact alone
>> doesn't mean they should be denied secure login if they are otherwse
>> bona-fide
>> members of your user community. (one DOES require secure UID:PWD match?)
>>
>> Quite the reverse - 'responsible' connectivity ISP may volunteer their
>> dynamic
>> pools to an RBL as it can help shut-down WinZombie routes to the outside.
>> Hopefully they also intercept port 25 but NOT port 587.
>> <snip>
>>
>> I hear you on responsible ISPs. Here is what I believe i have a problem
>> with:
>> When one of our users that "relays" mail thru one of our servers,
>> (connecting from a blacklisted ip address -ie in senderbase.org as POOR )
>> and the recipient is behind a Barracuda, we are finding that we (our mail
>> server addresses) are being blacklisted by Barracuda Central. Then we get
>> complaints from tons of users who can no longer send mail to anyone /any
>> net
>> using a Barracuda. We have separate servers for bulk mailing clients and
>> no
>> spam is allowed through our regular exim servers. We monitor our volumes
>> and
>> stats like mother hens. we have thousands of mail users -all of them
>> legit-(we are strictly a corporate provider) so this is becoming quite an
>> issue as we host mail services for companies worldwide- most have their
>> own
>> networks but some smaller accounts only have regular adsl with dynamic ip
>> provision. thoughts?
>> Bill
>
> Versteh.
>
> It is a bit off-the-wall, but similar to what can happen with even the
> best-maintained of closed-post mailing lists - possibly with a similar
> 'solution' as well...
>
> CAVEAT: it may break a few rules...
>
> What you describe sounds as if overly-aggressive far-end filters
> (Barracuda or
> otherwise) are boring down through *all* 'received' headers, AND NOT just
> the
> DNS credentials and envelope-from of the 'last mile' connecting server.
>
> IOW - they do not trust prior servers to have 'done the right thing'
>
> IF that is the correct assessment, (and it may not be), THEN 'what worked
> for
> us' - using Ecartis MLM as an example 'coz it is dead-easy - was to
> *archive*
> 100% of the incoming original, such that you have the pragmatic track-back
> capability (and perhaps legally-required one) needed...
>
> BUT then *strip all* prior headers, applying a 'fresh' set (only).
>
> Exim can do this also, though it needs more than just the equivalent of a
> box-tick Ecartis requires.
>
> And - I did say 'CAVEAT' - it violates some very basic smtp principles...
> some of which have *legal* standing in some jurisdictions.. with sharp
> teeth.
>
> Did I say 'CAVEAT'?
>
> But .. pragmaticaly - the paranoid far-end then 'sees' only your hopefully
> squeaky-clean server, AND NOT the sometimes-dodgy route over which a legit
> message had to travel to reach it.
>
> Note that this need not deny access to those unfortunate enough to be on a
> network OTHERWISE blackballed - so long as THEIR message is clean.
>
> It goes without saying that adopting any part of such an approach requires
> one
> to be more careful than ever that what they pass is NOT in any way nasty,
> ELSE
> Lybarger's corrolary to Sod's Law applies [1] - and you might as well plan
> to
> move domains and IP's every second day, if not keep a speedboat and extra
> passport handy.
>
> Me? Always happy to help the paranoid isolate themselves. Avoids
> potential
> axe-wounds.
>
> I'd just block the problematic destinations and advise those who bitched
> that
> there was no valid mailserver running there. Deal with that by fax, phone,
> dead-tree and postage stamp.
>
> Or Gmail. Who may yet serve all of us up an 'early retirement'.
>
> HTH,
>
> Bill
>
> [1] 'All else being equal, YOU LOSE'
>
>>>>>>>>>>>> YES.. we were thinking exactly the same thing but we have also
>>>>>>>>>>>> the same reservations... playing with headers seems somehow not
>>>>>>>>>>>> to sit right with us. But we honestly monitor our volumes very
>>>>>>>>>>>> carefully and jump on anyone that starts spamming thru our
>>>>>>>>>>>> 'regular' servers. We use the rrdtool graphing to monitor 24
>>>>>>>>>>>> hours per day ( we have an office in SE Asia that covers off NA
>>>>>>>>>>>> hours). We really our serious about maintaining a clean
>>>>>>>>>>>> reputation but barracuda is driving us nuts... have you heard
>>>>>>>>>>>> of anyone else having a problem with them?
> /bill
>
>
> --
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