Category: Technical

IPv6 and authentication

I just saw a post over on the mailop mailing list where someone had been bitten by some of the IPv6 email issues I discussed a couple of months ago. They have dual-stack smarthosts – meaning that their smarthosts have both IPv4 and IPv6 addresses, and will choose one or the other to send mail over. […]

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On Friday I talked a bit about the history behind TXT records, their uses and abuses. But what’s in a TXT record? How is it used? When and where should you use them? Here’s what you get if you query for the TXT records for from a unix or OS X command line with dig […]


A brief history of TXT Records

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, you look up {, A} and get back a couple of IP addresses. […]

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IPv6 Email is a little different

On Monday I talked about how big IPv6 address space is, and how many IPv6 addresses will be available to end users. We’re mostly an email blog, though, so what’s the relevance to sending email? If the recipient you’re sending to has an IPv6 mailserver you can send mail to them over IPv6, if you […]


IPv6 is big

IPv6 is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist, but that’s just peanuts to IPv6. The old Internet, the one you’re probably using right now, runs on IP version 4. IPv4 addresses have […]


Microsoft Send

Microsoft Send is a new mail client by Microsoft for iPhones and soon Windows Phone and Android phones. Send is designed to send quick, short messages to contacts. Instead of building a chat application build on a proprietary protocol, Send sends and receives its messages over email and uses your existing mailbox to handle the […]

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Image Blocking

I received this email earlier this week, an email that I wanted but this is how it arrived. The email contained a single image link, a text line of who the message was sent to, the senders name, address, and finally an unsubscribe link. Good news, the email is CAN-SPAM compliant! Bad news, I have […]

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PTR Records

PTR records are easy to over look and they have a significant impact on your ability to deliver mail without them.  Some ISP and mailbox providers will reject mail from IP addresses that do not have a PTR record created. PTR records are a type of DNS record that resolves an IP address to a […]

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Looking at the headers within the mail received with my Office365 domain I see dmarc=bestguesspass.  BestGuessPass?  That’s a new. A few days after seeing dmarc=bestguesspass, Terry Zink at Microsoft posted an explanation. Exchange Online Protection, the filtering system for Office365, is analyzing the authentication of incoming emails and if the domain is not publishing a […]

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What is the Mail From field?

When emails are sent, there are two from fields, the Mail From and the Display From address.  The Display From address (technically referred to as RFC.5322 from address) is the from address that is displayed to the end user within their email client.  The Mail From (technically referred to as RFC.5321 from address) is the […]

  • Ongoing Yahoo delays

    I've been hearing from folks over the last few days that they're seeing an uptick in deferrals from Yahoo! The deferrals are not uniform. ESPs report they're seeing some, but not all, customers affected. Other ESPs aren't seeing any changes. It's not just you. But it would be very worthwhile to dig into engagement and other stats. It's possible this is a new normal at Yahoo! and they're tightening filters to catch mail that doesn't fit their standards but was previously difficult to filter.No Comments

  • AOL starts using Sender Score Certification

    Good news for Sender Score Certified IPs. Return Path recently announced that AOL has joined the list of ISPs offering preferential treatment to certified IPs.  1 Comment

  • iCloud Service Disruption

    40% of iCloud users were affected this morning during a service disruption between 2:15AM and 9:30AM. Apple System StatusNo Comments