Re: [Asrg] misconception in SPF
Paul Smith <paul@pscs.co.uk> Sun, 09 December 2012 00:00 UTC
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Subject: Re: [Asrg] misconception in SPF
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On 07/12/2012 20:45, John Levine wrote: >> I think this makes sense, but I think it would make more sense if there was >> a way to just specify in the SPF record for, for example, twitter.com, that >> all legit senders for all subdomains are included in the highest level SPF >> record. > This sort of thing has been proposed before. It turns out that > anything in the DNS that starts "all names below this node ..." is > astonishingly hard to implement. Could we have a "direct parent" check rather than going up lots of levels? Eg, if you are having to fall back to an A record, look at the direct parent for a TXT record with appropriate data in So, if you are checking a message from xyz@bibble.twitter.com, you are doing your check back that bibble.twitter.com exists, and see that it only has an A record (if it has an MX record, that satisfies your checks). Now, you do a TXT lookup on 'twitter.com' and if the result has a record saying 'mx only' (or some such) you know that 'bibble.twitter.com' isn't valid as an email domain. This would be quicker than going up the tree, but would catch the most common case of having lots of hosts defined in a domain, any of which could be used for 'spoofing'. It would only be needed in the (hopefully, rare) case of having to fall back to the 'A' record. Checking for the TXT record would be slower than not doing so, but would be a lot more efficient than attempting to connect to a non-existent mail server at the A record. > I do agree that it would have been really nice if the SMTP fallback > from MX to A records had been deprecated and killed back in the 1980s. > I tried to get RFC 5321 not to add fallback to AAAA but the powers > that be insisted that it was already too late. > I wish it could be deprecated (but still required) now (ie, you MAY just have an A record to indicate where mail is to be delivered, but you SHOULD have an MX record instead). That way if we came across an A record only, we would have a stronger argument for persuading domain admins to add MX records. Currently some say 'well the standards say it's OK, so we're not changing anything'. It could be worth logging how many times we have to fall back to an A/AAAA record, AND the delivery succeeds - I may have a go at that ourselves. - Paul Smith Computer Services Tel: 01484 855800 Vat No: GB 685 6987 53
- Re: [Asrg] misconception in SPF John Levine
- [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF Derek Diget
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF Paul Smith
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF Andrew Sullivan
- Re: [Asrg] misconception in SPF Paul Smith
- Re: [Asrg] misconception in SPF darxus
- Re: [Asrg] misconception in SPF SM
- Re: [Asrg] misconception in SPF darxus
- Re: [Asrg] misconception in SPF Daniel Feenberg
- Re: [Asrg] misconception in SPF Paul Smith
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] various anti-spam techniques, was misc… John Levine
- Re: [Asrg] various anti-spam techniques, was misc… Rich Kulawiec
- Re: [Asrg] misconception in SPF SM
- Re: [Asrg] misconception in SPF Bill Cole
- Re: [Asrg] various anti-spam techniques, was misc… Christian Grunfeld
- Re: [Asrg] various anti-spam techniques, was misc… John Levine
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF Alessandro Vesely
- Re: [Asrg] misconception in SPF Bill Cole
- Re: [Asrg] misconception in SPF Paul Smith
- Re: [Asrg] misconception in SPF Andrew Sullivan
- Re: [Asrg] misconception in SPF SM
- Re: [Asrg] misconception in SPF Dave Crocker
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF Dave Crocker
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF Seth
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF Franck Martin
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] misconception in SPF Paul Smith
- Re: [Asrg] misconception in SPF Alessandro Vesely
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] misconception in SPF Dotzero
- Re: [Asrg] misconception in SPF Rich Kulawiec
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF Dave Crocker
- Re: [Asrg] misconception in SPF Chris Lewis
- [Asrg] whitelisting links (was Re: misconception … Dave Crocker
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] misconception in SPF Dave Crocker
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] whitelisting links (was Re: misconcept… Paul Smith
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] whitelisting links (was Re: misconcept… Martijn Grooten
- Re: [Asrg] whitelisting links (was Re: misconcept… darxus
- Re: [Asrg] misconception in SPF Eggert, Lars
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] whitelisting links (was Re: misconcept… Dave Crocker
- Re: [Asrg] whitelisting links (was Re: misconcept… Martijn Grooten
- Re: [Asrg] whitelisting links (was Re: misconcept… Michael Thomas
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF Chris Lewis
- Re: [Asrg] whitelisting links (was Re: misconcept… Paul Smith
- Re: [Asrg] whitelisting links (was Re: misconcept… Steve Atkins
- Re: [Asrg] whitelisting links (was Re: misconcept… Martijn Grooten
- Re: [Asrg] whitelisting links (was Re: misconcept… Dave Crocker
- Re: [Asrg] whitelisting links (was Re: misconcept… Martijn Grooten
- Re: [Asrg] whitelisting links (was Re: misconcept… Christian Grunfeld
- Re: [Asrg] whitelisting links (was Re: misconcept… Dave Crocker
- Re: [Asrg] whitelisting links (was Re: misconcept… Chris Lewis
- Re: [Asrg] misconception in SPF Alessandro Vesely
- Re: [Asrg] whitelisting links (was Re: misconcept… Paul Smith
- Re: [Asrg] whitelisting links (was Re: misconcept… Martijn Grooten
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] whitelisting links (was Re: misconcept… Rich Kulawiec
- Re: [Asrg] whitelisting links (was Re: misconcept… Michael Thomas
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] whitelisting links (was Re: misconcept… John Johnson
- Re: [Asrg] misconception in SPF John Johnson
- Re: [Asrg] whitelisting links (was Re: misconcept… Michael Thomas
- Re: [Asrg] whitelisting links (was Re: misconcept… John Levine
- Re: [Asrg] misconception in SPF Dotzero
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF Laura Atkins
- Re: [Asrg] DMARC, was misconception in SPF John Levine