Stuart D. Gathman wrote:
On Sun, 13 Jan 2008, Alessandro Vesely wrote:
> I've ended up making a blanket rule - no forwarding to AOL. Ever. For
> any reason - enforced by checking for aol.com in the MAIL TO for forwarded
> messages by the outgoing mail milter.
Obviously, senders want to maximize the chances that what they send gets
delivered. However, I hadn't thought that one would sacrifice forwarding
to specific domains in order to maximize the sum of its delivery chances.
As an alternative, you may register a domain that you only use for SPF-
compliant forwarding of unfiltered mail. That domain will end up having
the reputation it deserves, i.e. some average of the global spam traffic.
To let recipients make a better classification, you may opt to do vanilla
forwarding for senders that either lack any SPF policy or authorize your
IP explicitly --to achieve the same effect w.r.t. DNSBLs you need to use
a dedicated IP as well.
Doesn't help with AOL. They track reputation by IP (they don't check SPF). I
would need a another IP for forwarding unfiltered mail to AOL - and it would be
a waste because it would be very quickly blacklisted.
Thus it becomes apparent that SPF can help saving IPv4 addresses!
(In that respect, it is functionally similar to the "Host" HTTP header
and the "Server Name Indication" TLS extension.)
I mentioned you needed a dedicated IP. If the receiver that feeds your
forwarder is a client of the same DNSBL that blacklists it, that should
make for a good removal argument: it is enough if they blacklist the
original submitter. (AOL is peculiar in that it doesn't publish its
blacklist, AFAIK.)
Of course, it is technically unfeasible to forward mail keeping the
original sender's IP address. That is similar to the case where the
original sender's policy doesn't allow the forwarder to keep the same
envelope sender's domain. For both cases, the forwarder's problem is
how to indicate to blacklisters that the responsibility of the message
content should be associated with the original datum. For both cases,
blacklisters may contest the trustworthiness of the Received[-SPF]
headers written by forwarders.
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