Authentication Cheat Sheet

There are a several approaches to authenticating email, and the different authentication methods have a lot of different settings to choose from (sometimes because they’re useful, other times just because they were designed by committee). It’s nice that they have that flexibility for the complex situations that might benefit from them, but almost all the time you just want to choose a good, default authentication approach.
So here’s some short prescriptive advice in no particular order for “how to do email authentication at an ESP well” without the long discussions of alternative approaches and justification of each piece of advice.

  1. Remove every trace of DomainKeys from your email flow
  2. Sign all your email with DKIM
  3. Publish SPF records
  4. Have your SPF records finish with ~all, not -all
  5. Ignore SenderID, unless you have delivery problems at Hotmail (and even then measure results rather than just assuming it will help)
  6. Don’t publish ADSP records
  7. Have the customer pick a single domain to tie their reputation to – ideally their “main” domain, but if that’s not possible then a customer-specific domain owned by the ESP is the next best thing (i.e. “customer.com” is ideal, but “customer.esp.com” is much better than just “esp.com”)
    1. Use that domain as the d= field when signing email (“d=customer.com”)
    2. Use that domain, or a sub-domain of it, in the From: field of the email (“From: Someone <someone@customer.com>” or “From: Someone <someone@fooble.customer.com>”)
  8. Pick a good email address to use in the From: field, don’t change it lightly
  9. Use two-part selectors for DKIM, one specific to you, the ESP, on the right and one for key rotation on the left (why do this?)
  10. Use just what’s needed for DKIM – don’t use i=, l=, q=, x= or z= in the signature, don’t use g= or s= in the published key
    1. dkimcore.org has more specific advice about which subset of DKIM to sign with
  11. Make sure your SPF records are valid
  12. TLS/SSL isn’t useful for authenticating mail (it’s great for connecting to a smarthost from a mail client, but not for connections from the smarthost)
  13. None of SPF, DKIM or TLS are really designed to protect or hide the contents of a message
    1. Customers who really want that could look at S/MIME or PGP
    2. … but better to design their business model such that they don’t need to, as client support is spotty at best
  14. Empirical evidence that doing something will make a customer happy trumps any of the above
    1. maybe because there’s evidence SenderID or ADSP or somesuch really helps that customer
    2. or maybe because the customer just wants it, even if there’s no evidence it would help

Mail client use of authentication data is still in flux, so it’s likely that some of this may change slightly (interaction between SPF and DKIM d= domains, for example) but it’s a pretty good base to start with today.

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Authentication and phishing

Yahoo announced today that they are releasing the Yahoo! Mail Anti-Phishing Platform (YMAP) that will help protect their users from phishing. They have a similar project in place for eBay and PayPal mail, but this will extend to a broader range of companies.

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Would you buy a used car from that guy?

There are dozens of people and companies standing up and offering suggestions on best practices in email marketing. Unfortunately, many of those companies don’t actually practice what they preach in managing their own email accounts.
I got email today to an old work email address of mine from Strongmail. To be fair it was a technically correct email. Everything one would expect from a company handling large volumes of emails.  It’s clear that time and energy was put into the technical setup of the send. If only they had put even half that effort into deciding who to send the email to. Sadly, they didn’t.
My first thought, upon receiving the mail, was that some new, eager employee bought a very old and crufty list somewhere. Because Strongmail has a reputation for being responsible mailers, I sent them a copy of the email to abuse@. I figured they’d want to know that they had a new sales / marketing person who was doing some bad stuff.
I know how frustrating handling abuse@ can be, so I try to be short and sweet in my complaints. For this one, I simply said, “Someone at Strongmail has appended, harvested or otherwise acquired an old email address of mine. This has been added to your mailing list and I’m now receiving spam from you. ”
They respond with an email that starts with:
“Thank you for your thoughtful response to our opt-in request. On occasion, we provide members of our database with the opportunity to opt-in to receive email marketing communications from us.”
Wait. What? Members of our database? How did this address get into your database?
“I can’t be sure from our records but it looks like someone from StrongMail reached out to you several years ago.  It’s helpful that you let us know to unsubscribe you.  Thank you again.”
There you have it. According to the person answering email at abuse@ Strongmail they sent me a message because they had sent mail to me in the past. Is that really what you did? Send mail to very old email addresses because someone, at some point in the past, sent mail to that address? And you don’t know when, don’t know where the address came from, don’t know how it was acquired, but decided to reach out to me?
How many bad practices can you mix into a single send, Strongmail? Sending mail to addresses where you don’t know how you got them? Sending mail to addresses that you got at least 6 years ago? Sending mail to addresses that were never opted-in to any of your mail? And when people point out, gently and subtly, that maybe this is a bad idea, you just add them to your global suppression list?
Oh. Wait. I know what you’re going to tell me. All of your bad practices don’t count because this was an ‘opt-in’ request. People who didn’t want the mail didn’t have to do anything, therefore there is no reason not to spam them! They ignore it and they are dropped from your list. Except it doesn’t work that way. Double opt-in requests to someone has asked to be subscribed or is an active customer or prospect is one thing. Requests sent to addresses of unknown provenance are still spam.
Just for the record, I have a good idea of where they got my address. Many years ago Strongmail approached Word to the Wise to explore a potential partnership. We would work with and through Strongmail to provide delivery consulting and best practices advice for their customers. As part of this process we did exchange business cards with a number of Strongmail employees. I suspect those cards were left in a desk when the employees moved on. Whoever got that desk, or cleaned it out, found  those cards and added them to the ‘member database.’
But wait! It gets even better. Strongmail was sending me this mail, so that they could get permission to send me email about Email and Social Media Marketing Best Practices. I’m almost tempted to sign up to provide me unending blog fodder for my new series entitled “Don’t do this!”

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Gmail shows authentication data to the recipient

Yesterday Gmail rolled out some changes to their interface. One of the changes is that they are now showing end users authentication results in the user screen.
It’s really the next step in email authentication, showing the results to the end user.
So how does Google do this? Google is checking both SPF and DKIM. If mail is authenticated and the authentication matches the from address then they display the email as:
mail from steve to me
If we click on “details” for that message, we find more specific information.
full details of message showing signing domain and spf domainIn this case the mail went through our outgoing mailserver to gmail.
Mailed-by indicates that the message passed SPF and that the IP address is a valid source of mail from wordtothewise.com.
Signed-by shows the domain in the DKIM d=. In this case, we signed with the subdomain dt.wordtothewise.com. That’s what happens when you sign using the domain in the From address (or a subdomain of it).
For a lot of bulk senders, though, their mail is signed using their ESP’s domain instead.  In that case Gmail shows who signed the mail as well as the from address.

And when we click on “details” for that message we see:
3rd party signature detailsThis is an email from a sender using Madmimi as an ESP. Madmimi is handling both the SPF authentication and the DKIM authentication.
As an aside, this particular  sender has a high enough reputation that Gmail is offering me an unsubscribe option in their interface.
Gmail is distinguishing between first party and third party signatures in authentication. If the mail is authenticated, but the authentication appears to be handled by a separate entity, then Gmail is alerting recipients to that fact.
What does this mean for bulk senders?
For senders that are signing with a domain that matches their From: domain, there is no change. Recipients will not see any mention of your ESP in the headers.
However, if you are using an ESP that is signing your mail with a domain they own, then your recipients will see that information displayed in the email interface. If you don’t want this to be displayed by Gmail, then you will need to move to first party signing. Talk to your ESP about this. If they’re unsure of how to manage it, you can point them to DKIM Core for an Email Service Provider.
Gmail blogpost about the changes
Gmail help page about authentication results

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