A brief history of TXT Records

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When the Domain Name System was designed thirty years ago the concept behind it was pretty simple. It’s mostly just a distributed database that lets you map hostname / query-type pairs to values.
If you want to know the IP address of cnn.com, you look up {cnn.com, A} and get back a couple of IP addresses. If you want to know where to send mail for aol.com users, you look up {aol.com, MX} and you get a set of four hostname / preference pairs back. If you want to know the hostname for the IP address 206.190.36.45 you look up {45.36.190.206.in-addr.arpa, PTR} and get a hostname back.
There’s a well-defined meaning to each of those query types  – A is for IP addresses, MX is for mailservers, PTR is for hostnames – and that was always the intent for how DNS should work.
When DNS was first standardized, though, there was one query type that didn’t really have any semantic meaning:

TXT RRs are used to hold descriptive text. The semantics of the text depends on the domain where it is found.

TXT records didn’t really have a use. Some domain owners used them to provide their contact information for the domain, and there were some funny messages scattered around, but that was about it.
Around the year 2000 email people started thinking about publishing data in the DNS. Email people are not the same as DNS people. To a DNS person the obviously correct way to do that would be to define a new query type, persuade people to agree on that definition and then make it a standard by publishing an RFC.
But email people have a long history of piling standards on top of other standards and deploying ad-hoc approaches (e.g. X-Headers, Uuencoding, PGP encapsulation and ascii armoring) without more than the bare minimum of agreement on the right way to do things. That approach helps with fast-yet-gradual deployment of new solutions, but also leads to a certain impatience with the bureaucracy of an actual standards development process.
“Just stick it in a TXT record!” became the rallying cry.
SPF was the first widely deployed protocol to do that. There was an attempt to migrate SPF from using TXT records to using a dedicated SPF record type, but given the deployed base of users already using TXT records it was doomed to failure.
Whenever someone is rolling out a new protocol that needs a domain owner to publish something – whether it’s something fairly standardized or pretty much ad-hoc – they tend to reach for a TXT record.
Some more things you need to know about TXT records on Monday.

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Spam, Phish or Malware?

Some mornings I check mail from my phone. This showed up this morning.
PizzaHutMail
My first thought was “oh, no, Pizza Hut is spamming, wonder who sold them my address.”
Then I remembered that iOS is horrible and won’t show you anything other than the Friendly From and maybe it was some weird phishing scheme.
When I got to my real mail client I checked headers, and sure enough, it wasn’t really from Pizza Hut. I’m guessing actually malware, but I don’t have a forensics machine to click the link and I’m not doing it on anything I can’t wipe (and have isolated from the rest of my network).
The frustrating thing for me is that this is an authenticated email. It not from Pizza Hut, the address belongs to some company in France. Apparently, that company has had their systems cracked and malware sent through them. Fully authenticated malware, pretending to be Pizza Hut, and passing authentication on various devices.
Pizza Hut isn’t currently publishing a DMARC record, but in this case, a DMARC record for Pizza Hut wouldn’t matter. None of the email addresses in the headers point to Pizza Hut.
I spent last week listening to a lot of people discussing DMARC and authentication and protecting people from scams and headers. But those all the protocols in the world won’t protect against this kind of thing. Phishing and malware can’t be fixed by technology alone. Even if every domain on the planet published a p=reject policy, mail like this would still get through.
 
 
 

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Office365/EOP IPv6 changes starting today

Terry Zink at Microsoft posted earlier this week that Office365/Exchange Online Protection will have a significant change this week. Office365 uses Exchange Online Protection (EOP) for spam filtering and email protection. One of the requirements to send to EOP over IPv6 is to have the email authenticated with either SPF or DKIM.  If the mail sent to Office365/EOP over IPv6 is not authenticated with SPF or DKIM, EOP would reject the message with a 554 hard bounce message.  Most mail servers accept the 554 status code and would not retry the message.  After multiple 5xx hard bounces to an email address, many mail servers would unsubscribe the user from future email campaigns.  The update starting today April 24, will change the error status code for unauthenticated mail to EOP from a 554 hard bounce to a 450 soft bounce and a RFC-compliant and properly configured mail server would then retry the message.
Prior to April 24, 2015, EOP responds to unauthenticated mail with a status code of: “554 5.7.26 Service Unavailable, message sent over IPv6 must pass either SPF or DKIM validation”.

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DMARC: an authentication framework

A new email industry group was announced this morning. DMARC is a group of industry participants, including large senders, large receivers and relevant intermediaries working on a framework to reduce the harm from phishing.
DMARC is working on a standard to allow senders to publish sending policies and receivers to act on those policies. Currently, senders who want receivers to not deliver unauthenticated email have to negotiate private agreements with the ISPs to make that happen. This is a way to expand the existing programs. Without a published standard, the overhead in managing individual agreements would quickly become prohibitive.
It is an anti-phishing technique built on top of current authentication processes. This is the “next step” in the process and one that most people involved in the authentication process were anticipating and planning for. I’m glad to see so many big players participating.
 

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