[Mailman-Developers] DNS and mailing lists -- an idea

J C Lawrence claw@kanga.nu
Sun, 25 Nov 2001 00:04:34 -0800

On Sun, 25 Nov 2001 00:22:39 -0500 
Jay R Ashworth <jra@baylink.com> wrote:

> It occurred to me, riding home tonight from a concert and doing
> the After Action in my head from the whole fiasco, that there
> might be something productive in a script that could crawl the
> pending mail log looking for signs that some large batch of mail
> is pending for bad reasons.  

Which is a generically Good Thing.  In larger installations I like
to move spool entries for slow MX'es off the main production MTA and
off to a box specifically configured for handling slow MXes (I do
domain routing on the primary MX for the one's I've already

> Caching accidents happen to everyone occasionally... 

Frankly: Never seen one.  Certainly not on a client end.
Experiences like yours, sure, but that's a rather different deal.

> and if one happens to your list with 4000 people on AOL, it could
> get ugly.

Quite.  It would hurt most lists if the auto-unsubscribed AOL as
bouncing due to, say, bad DNS (which could happen thru simple route
flaps/'net connectivity problems on *your* end).

> If such a script could restart the associated name daemon,
> flushing it's cache, it would save a lot of delay and concern for
> various groups of people, I think.  Assuming you could create a
> good heuristic for deciding when to dump the cache... which
> shouldn't be too hard, since a false dump isn't too painful.

Actually I use pdnsd which keeps a copy of its cache on disk, so
restarts get the same cache as before...

More simply, I don't see this buys you anything.  If AOL is not
reporting it won't be in your cache.  Non-answers are not cached,
only valid mappings are cached.  

> So, am I missing something obvious here?  Will an MTA *without* a
> caching server actually be affected less (because it's making
> direct lookup calls to the zone servers in question)?  It's an
> area, admittedly, in which I'm a touch weak... which is why I'm
> asking y'all.

Typically the local nsd will do a certain amount of local cacheing
(usually the last response or two) within the current application
scope.  Certain MTAs will (or can be configured to) cache the MX
lookups in the spool files (a generally Bad Idea, but it can be a
savings in heavily loaded cases)..

J C Lawrence
---------(*)                Satan, oscillate my metallic sonatas.
claw@kanga.nu               He lived as a devil, eh?
http://www.kanga.nu/~claw/  Evil is a name of a foeman, as I live.