Re: SPF and bouncing

On Sat 07/Apr/2012 13:36:48 +0200 Michael Deutschmann wrote:
> 
> "Is it okay, on the modern internet, to assume that legitimate bounce
> messages between bailiwicks will not occur?"

I'd say no, because of the better-cause-deserving diligence that some
organizations put in making sure that the envelope sender is kept
unaltered on forwarding to external mailboxes.  That policy is
supported by "alias expansion" as standardized by SMTP.

> (One idea is to use SPF-checked HELO and/or rDNS to at least get a domain
> that can be coarsely checked against the whitelist.  But that can easily
> fail, especially if the sending IP is a smarthost for many domains.)

IMHO it makes sense to require that such kind of forwarders have at
least a good helo identity, I mean accompanied by an SPF record.  Then
checkers must not reject if they have malfrom->fail and helo->pass.