On Mon, Feb 03, 2003 at 03:34:33PM -0500, Wietse Venema wrote:

> > Postfix here is having occasional DNS timeout problems.
> >
> > It's caching DNS forwards through a couple of private
> > chained DNS servers before hitting the public's DNS servers.
> >
> > Some of the public's DNS servers are occasionally a bit slow to respond,
> > and some of those use short expiry intervals, so the MX and A data isn't
> > always cached locally.
...
> > And therefore statically linked
> > Postfix binaries would need to be relinked with a new libresolv.a
> > library whose RES_TIMEOUT has been increased?
>
> Neither FreeBSD 4.7 nor 7.3 document RES_TIMEOUT.

Furthermore, I think it's a bad idea for many sending sites to be making
adjustments to accomodate a receiving site that is configured in an
unreliable manner. Any mail-receiving site that sets its DNS ttl values
to less than a few hours is essentially declaring that it it doesn't
want to receive mail from everybody. I don't think we should encourage
this attitude. I set my ttl values low sometimes -- when I am in the
middle of making many changes --- and then only as low as 1 hour. Then
they go back up to 12 or 24 hours.

Very low ttl values should only be set for load-balanced intractive
destinations such as web sites where there is no queuing mechanism and
uesrs don't mind an occasional timeout and a manual reload. It makes
absolutely no sense to set ttl values for MX records to any lower than a
few hours, and perhaps one hour temporarily.

Rahul

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