Heiko Schlittermann wrote:
>
> Anyway - what about implementing the fallback_hosts feature not for
> temporary errors but for 5xx errors too?
>
> The rationale: There's a mail server sending from non-rDNS-able address.
> On most connections it works, but some reject this server with 5xx. In
> this, *only* this case I'd like to route the mails to some friendly
> smarthost...
>
> (The smart host uses callout for recipient checks, so if the 5xx is
> because of some other reason, it should reject the mail at SMTP time
> already, thus refusing its smart service.)
>
> Could please somebody explain me, why it's a stupid idea? ;-)
This has been discussed ad nauseam many times in the past. It will _not_
give you a reliable mail server even if implemented. A large number of
sites do not reject blacklisted messages with 550's, but rather
quarantine or blackhole them. So implementing this feature will have all
the negatives of violating the RFCs, and none of the intended benefits.
http://www.google.ca/search?q=site:www.exim.org/mail-archives+fallback+OR+retry+smarthost&hl=en&lr=&start=10&sa=N
- Marc
