Re: [exim] retry data of multiple MX

On Wed, 2006-05-03 at 14:04 +0200, Daniel Tiefnig wrote:
> Patrick Okui wrote:
> > I'd agree with you if both the MX hosts had equal priority, but in
> > this case I do not see why exim should try to deliver to
> > mailbackup.inode.at unless there are reachability issues in
> > contacting mail.rtr.at.

a (temporary) failure is a (temporary) failure, no matter at which stage
in the SMTP dialogue you are (connect, banner, EHLO, MAIL FROM, RCPT TO,
DATA). the relevant excerpt from RFC 2821 is:

When the lookup succeeds, the mapping can result in a list of
alternative delivery addresses rather than a single address, because
of multiple MX records, multihoming, or both. To provide reliable
mail transmission, the SMTP client MUST be able to try (and retry)
each of the relevant addresses in this list in order, until a
delivery attempt succeeds. However, there MAY also be a configurable
limit on the number of alternate addresses that can be tried. In any
case, the SMTP client SHOULD try at least two addresses.

> And I'd agree with that, if exim would not try to deliver to
> mailbackup.inode.at (after a temporary error for user@???) at all.
> But it only does not try the secondary MX if the primary MX failed "for
> a very long time"(tm). And that gives very bad behaviour with a
> greylisting MX and a not-greylisting backup MX. (Besides that being a
> very stupid setup, yes.)

well, the retry hint is quite correct, mail.rtr.at hasn't accepted
e-mail to the domain for weeks, which is quite silly behaviour for a
primary MX. the administrator for rtr.at won't get reliable e-mail
service until he fixes his configuration.

on the other hand, the RFC does say that an MTA SHOULD try at least two
addresses, and Exim doesn't do that here.
--
Kjetil T.