Email supports TLS (Transport Layer Security), what we used to call SSL. Unlike the web, which split it’s TLS support off into a completely different protocol – https, listening on port 443 vs http listening on port 80 – SMTP implements it inside it’s non-encrypted protocol. A mailserver advertises that it supports this by having the word “STARTTLS” in the...
I’m repeating the presentation I gave at M3AAWG in London for the Certified Senders Alliance.It’s all about how to send an email by hand, and how knowing the mechanics of how an email is sent can help us diagnose email delivery issues.We’re starting in about five hours from when I post this.Register at
The nice folks over at Postmark shared a new deliverability resource last week. The SMTP Field Manual. This is a collection of SMTP responses they’ve seen in the wild. This is a useful resource. They’re also collecting responses from other senders, meaning we can crowdsource a useful resource for email deliverability folks.
As the volume and severity of malicious email increases, filters are increasingly following links in emails. This is really nothing new. Barracuda and other filters have been inspecting links automatically for years. From what I’ve seen there does seem to be some level of risk analysis based on domain reputation. That makes sense, not only is following links computationally expensive, it...
Bounces and bounce handling is one of those topics I’ve avoided writing about for a long time. Part of my avoidance is because there are decades of confusing terminology that hasn’t ever been really defined. Untangling that terminology is the first step to being able to talk sensibly about what to do. Instead of writing a giant long post, I can break it into smaller, more focused...
It’s rare I find mail that violates the SMTP spec (rfc5321 and rfc5322). I’ve even considered removing “send mail from a correctly configured mail server” from my standard Best Practices litany. But today I got mail asking me to respond to a survey. This whole email is a mess of problems, and it’s claiming to be from the California Secretary of State. It’s...
My first access to “the internet” was through a dialup modem on a VAX at the FDA. I was a summer intern there through my college career and then worked full time after graduation and before grad school. My email address ended in .bitnet. I could mail some places but not others. One of the places I couldn’t send mail was to my friends back on campus. A few of those friends were...
Happy 2016! We started off the year with a few different “predictions” posts. As always, I don’t expect to be right about everything, but it’s a useful exercise for us to look forward and think about where things are headed. I joined nine other email experts for a Sparkpost webinar on 2016 predictions, which was a lot of fun (see my wrap up post here), and then I wrote a long post about security...
An old blog post from 2013, that’s still relevant today. “Blocked for Bot-like Behavior” An ESP asked about this error message from Hotmail and what to do about it. “Bot-like” behaviour usually means the sending server is doing something that bots also do. It’s not always that they’re spamming, often it’s a technical issue. But the technical problems make the sending server look like a bot...
Earlier today I approved a comment from Mike on a post about problems at AOL from 2012. The part of the comment that caught my attention: SMTP error from remote mail server after end of data: 521 5.2.1 : AOL will not accept delivery of this message. Mike also mentioned his IP reputation is good, when he checks at AOL so he doesn’t understand why mail is being blocked. I think the big clue...
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