Bailo, John wrote:

Wouldn’t a valid DomainKeys indicate the mail is not spam.

Domain Keys and DKIM try to provide some assurance that the sender is who they claim to be. That's it -- no assertion is made about the contents, just the identity of the sender.

Don't despair because this is very important -- it's only after you can be certain that you can tell which messages are really from that you can start to build a reputation for them. Once you know always uses DK/DKIM and they are responsible email senders, you can think about automatically quarantining/discarding anything claiming to be from that fails those checks. And you can do it without wasting a lot of CPU cycles on complicated spam detection techniques...

Blacklists are shortcuts used to block spam. If a sender/host is listed on one you (the receiver) trust, you may choose not to accept the message or to discard it. But not appearing on a blacklist just means your message can't be pre-judged -- most recievers will just start examining the incoming message to see if it can be classified as spam or not based on other factors.

So as a sender, even though you've implemented DK you still have to pay attention to how your message will be viewed by spam filters. Do your messages include clickable links to domains other than the sending address in the From: header? That may increase the likelihood of your message being scored as spam. Using a lot of "sales-y" words with exclamation points? You've probably increased your score a little more. If that score gets too high you could wind up in the spam folder even if you pass SPF, Sender-ID, DK and DKIM checks every time.

Sorry if this feels remedial, but it seems like there are folks on the list who will benefit from a reminder of what sender authentication techniques will and won't do for you. Maybe one of these days I'll post this and other tidbits somewhere for reference...