Ned Freed <NED(_at_)innosoft(_dot_)com> writes:
Such problems can remain dormant for years before some type of outage
brings them to light. This proposal has the effect of increasing the
number of cases where fallback routing will be used, which will inevitably
result in an increase in this sort of behavior.
I'm having a hard time understanding your position. Some sites
implement MX records incorrectly, so you want to discourage the use of
MX records?
I've had problems where the first-contacted MX for a domain was issuing
4XX replies for some reason and clients were not rolling over to some
other MX (either co-primary or secondary).
There is also the added complexity involved in caching errors.
This problem exists independently of MX fallbacks. Without MX
fallbacks, the mail gets delayed instead of suboptimally delivered.
I have some possible advice on this subject (don't cache anything
you get after issuing a MAIL command) but that's more informed
supposition than implementation experience.
If we're going to run around fixing these old versions to handle
this right we need to take care of their problems handling proper
pruning of MX lists.
Sendmail 8 already falls over to the next MX when it gets a 4XX reply
code. It also does MX randomization and MX piggybacking. It does do
proper pruning of MX lists and I believe it has done so for quite some
time.
--
_.John G. Myers Internet: jgm+(_at_)CMU(_dot_)EDU
LoseNet: ...!seismo!ihnp4!wiscvm.wisc.edu!give!up