Victor Duchovni:
> Yes.
>
> > 2) Am I accurate in assuming that smtp.receivingdomain.com will see delivery
> > attempts from both IP addresses for mailer.sendingdomain.com and
> > fallbackmailer.sendingdomain.com, and therefore I will need to manage the
> > Sender Reputations of both IPs, make sure they are both included in FBLs,
> > absent from blacklists, etc.?
>
> Yes.
>
> > 3) Won't this cause an issue with DKIM validation? If the original message
> > was signed by mailer.sendingdomain.com, won't it fail validation on the
> > receiving end since the fallback relay has a different hostname? If so, any
> > possible solutions to this?
>
> DKIM does not care about the sending host. It is an end-to-end protocol,
> not a hop-by-hop protocol. Your need to take some time to understand DKIM.
>
> DKIM authenticates the responsible (d=) domain, via a cryptographic
> signature on the message whose public key is available via DNS. DKIM
> messages are authentic regardless of which host sends them. The signature
> authenticates the content, not the transmission channel.
SPF binds the sending domain to IP addresses, so you may want to
list the graveyard machine there.
Wietse
