TagSMTP

New Deliverability Resource

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.

Automated link checking getting more sophisticated

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...

What’s a bounce?

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...

Send Actual SMTP

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...

The history of email

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...

January 2016: The Month in Email

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...

Following the SMTP rules

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...

When did the reject happen?

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...

Confusing the engineers

We went camping last weekend with a bunch of friends. Had a great time relaxing on the banks of the Tuolumne River, eating way too much and visiting. On Saturday I was wearing a somewhat geeky t-shirt. It said 554: abort mission. (Thank you MessageSystems). At some point on Saturday every engineer came up to me, read my shirt and then looked at me and said “That’s not HTTP.”...

Email is inherently a malicious traffic stream

It’s something many people don’t think about, but the majority of the traffic coming into the SMTP port is malicious. Spam is passively malicious, in that it just uses resources and bothers people. But there is a lot of actively malicious traffic coming into the SMTP port. Email is used as a vector to spread viruses and other malware. Email is also used for phishing and scamming. Many...

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