In message <20140725031019.24785.qm...@f5-external.bushwire.net>, "Mark Delany"
writes:
> On 24Jul14, Kevin Darcy allegedly wrote:
> > So, if the TTL on the record were higher than the queue-expire setting
> > of the MTA, wouldn't the *intelligent* strategy be to promote the
> > tempfail to a permfail?
>
> Most SMTP clients use a DNS cache so they have no idea what the
> original TTL is.
>
> Even if they could see the auth TTL you'd have to worry about domains
> that just happen to have very large TTLs in place today for whatever
> reason. How do you differentiate those domains?
>
> As far as standardizing such an idea, I'd hazard a guess that the IETF
> would not look kindly on encoding semantics into TTL values. Your
> rationale for this approach would need to be pretty compelling.
>
> > I've never written an MTA, but it seems like an
> > obvious optimization to me.
>
> It's surprising how hard it is to get the TTL out of most DNS client
> libraries. None of the gethostby* family return it. Even fancy
> libraries like c-ares are hit and miss with making the TTL available
> for different RR types.
>
> And of course the whole thing implies changing every SMTP client on
> the planet to recognize these large TTLs. That's a bit of work.
>
> All in all it's hard to see what this approach achieves compared to
> nullmx which works today with no code changes and does not require any
> special interpretation of DNS data.
0.0.0.0 and :: are orthognal to MX 0 .
One means "I am a host, I exist, but I don't know my/have
a address" presumably because it is offline, the other means
"There is no SMTP service for this domain". One is temp
fail for SMTP, the other is a permanent fail.
> Mark.
>
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--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: ma...@isc.org
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