Re: [Asrg] VPNs (was: request for review for a non FUSSP proposal

Rich Kulawiec <rsk@gsp.org> Mon, 29 June 2009 12:08 UTC

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Date: Mon, 29 Jun 2009 08:08:26 -0400
From: Rich Kulawiec <rsk@gsp.org>
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Subject: Re: [Asrg] VPNs (was: request for review for a non FUSSP proposal
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On Thu, Jun 25, 2009 at 01:37:46PM +0200, Alessandro Vesely wrote:
> AFAIK, there is no way SMTP can be configured so that a given sending  
> location can be whitelisted. One can try and detect what MTA sends the  
> message and whitelist specific filters, presumably doing detection by  
> the IP address of each mailout. That's much like VPN: being at a higher 
> level doesn't ease the task. For example, assume someone trusts Gmail's 
> egress filtering and wants to skip content filtering for mail coming from 
> there. What work is required to accomplish (and maintain) that task, on 
> typical MTA software?

Yes, MTAs can be configured so that a given sending location -- that is,
IP address -- is whitelisted.  I do it all the time.  But it's not a
very good solution, and it doesn't scale.  Moreover, it's brittle: if the
sender's outbound mail server changes its address, then it stops working.
Conversely, if someone else acquires that server's previous address,
then it starts working for someone I didn't intend it to work for.

Level of work?  I think, roughly speaking, it's one or two lines of
configuration with most MTAs.  But (as I think you're pointing out) the
actual configuration itself isn't the issue: it's the time and effort
that it takes to figure out what should be in the configuration, and
then to maintain it.

---Rsk