Pierre A. Humblet wrote:
> Exim already has a "fallback on defer" feature through the use of
> the "fallback_hosts" list.
>
> The patch below adds 4 lines to exim to enable "fallback on fail"
> as well, under control of the configuration file. It has no impact
> on existing installations.
>
> It would be nice if this patch (or a variation) was included in exim.
> I believe that RFC 2821 allows this feature, as discussed below.
>
> 4.2.1 Reply Code Severities and Theory
> 4yz Transient Negative Completion reply
> <snip>
> A rule of thumb to determine
> whether a reply fits into the 4yz or the 5yz category (see below)
> is that replies are 4yz if they can be successful if repeated
> without any change in command form or in properties of the sender
> or receiver (that is, the command is repeated identically and the
> receiver does not put up a new implementation.)
>
> Thus a 5yz reply does not imply that the commands will fail if repeated
> to a receiver with new properties. 5yz is "permanent" only with respect
> to a specific receiver implementation. The "fallback on fail" feature
> should only be used when there are reasons for the fallback host to have
> an implementation that should accept the mail.
Argh! No!
I am so pissed off with certain broken Novell systems ignoring our 5xx
responses and hitting each of our MX's in turn for the same nonexistent
username. Please don't encourage this behaviour. 5xx means NO.
- Jeremy
