Re: [Exim] MX Record points to non-existent host

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Author: Greg Louis
Date:  
To: Exim Users Mailing List
Subject: Re: [Exim] MX Record points to non-existent host
On 20030222 (Sat) at 2152:32 +0000, Matthew Byng-Maddick wrote:
> I already sent you a mail off-list about this, but I'll answer this on
> list because actually I think it's an important enough point to make.
>
> I'm also scared that I'm agreeing with the most.weird one. :-)


Chuckle. Actually I do too, were it not for the Scylla-and-Charybdis
thing I wrote to you about privately.

> > What I would like is for my MTA to tolerate as much error as possible
> > on the other end while behaving perfectly in every other respect.
>
> But you're decreasing the reliability of your own software, by introducing
> complexity in it that makes it harder to audit, harder to spot the subtle
> interactions between all these human-error correcting bits of code. The
> simpler the code that handles my email, the more likely it is that my
> email gets from A to B and doesn't get lost somewhere in the middle. What
> you're actually doing is increasing the ability of communication, while
> potentially decreasing it for everyone else, and hoping that the changes
> you're making won't fail catastrophically where your edge cases occur.


I could argue that tolerance ought to be part of the behavioral
requirement, and that the software should be as simple as possible but
no simpler. But let's not get into that for now; basically, we are in
agreement.

Call that Scylla. Then Charybdis is, unless most everybody at once
decides to refuse to handle mail from or to noncompliant MTAs, anyone
who takes that initiative is putting his users at a decided
disadvantage. My employer would not tolerate my doing that, though
it's generally a quite public-spirited company.

Charybdis seems nearer and more threatening than Scylla.
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