> > > Ideally, you would have all your users use your mailserver. > > > >How can you force this? > > By saying "People that use an E-mail address on our domain must > send E-mail through our mailserver."
OK - how do I force them to do this with Imail?
It's impossible. You force it with the policy. If someone disobeys, their E-mail may or may not be delivered.
> The SPF record that you publish is used by anyone using SPF, not just > Declude JunkMail. So if you publish "v=spf1 +mx ?all" ...
I fail to see how I or anyone else will benefit to any worthwhile degree by me publishing SPF records with the ?all flag.
Because any E-mail sent from your domain and your mailserver will be whitelisted (the "+mx" does that). People who send mail using your domain, but not your mailserver, will not benefit. That is by design. If they want to benefit, they use your mailserver.
Others benefit by the reduced false positives (if you send them mail from your domain and your mailserver, it will not get blocked, even if it otherwise might have).
Granted, the test will currently PASS because of my ip4:203.132.253.0/24 but spammers will never be
allowed to use that range so spammers will still get away with the UNKNOWN
result.
Correct. And that is what you want, since you can't control your users. If/when you can control your users, and force them to use your mailserver, you can then use -all, so mail from spammers using your domain will be blocked. That's even better.
In the meantime, spammers will have their mail blocked normally (using IP-based and other spam tests). So with the "+mx ?all", spammers do not benefit, and some of your users do benefit (by having their mail whitelisted).
Think of it this way -- with SPF, all domains start off with "?all" (an UNKNOWN result for anyone using that domain). If nobody publishes SPF records, all E-mail has a result of UNKNOWN, and spam control is exactly the same as it is without SPF. If a domain adds "+mx ?all", then all of a sudden false positives are reduced (as E-mail from that domain and sent from an IP in the MX record is now whitelisted), but nothing else is affected. If a domain adds "+mx -all", then the false positives are reduced *and* spam detection is improved (as spam sent using the domain will now get blocked). So any SPF record that is thought out properly will improve spam detection, either by reducing false positives or improving spam detection.
-Scott
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