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Category: Technical

Link tracking redirectors 2

It’s not too difficult to build your own link redirector, perhaps a few hours work for a basic implementation me, yesterday Yesterday I suggested that link tracking wasn’t too complex, but didn’t really have anything to back the claim up. And nobody trusts developer time estimates. So I cranked DEF CON Radio and wrote a […]

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Link tracking redirectors

Almost every bulk mail sent includes some sort of instrumentation to track which users click on which links and when. That’s usually done by the ESP rewriting links in the content so they point at the ESP’s tracking server, and include information about the customer, campaign and recipient. The recipient clicks on the link in […]

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Gradual DMARC Rollout

Over on twitter Alwin de Bruin corrected me on an aspect of DMARC soft rollout I’d entirely forgotten about. It’s useful, so I thought I’d write a quick post about it. If you have a large mail stream and you want to avoid the Scary Red Flag Day when you turn on DMARC p=reject enforcement […]

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Why do my URLs have two dots?

You take a turn, I take a turn At the SMTP level email is very much a simple line-by-line text based protocol. The client sends a command on a single line, the server responds with one or more lines (the last one marked by having a space in the fourth column), and then the client […]

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Captchas

Captchas – those twisty distorted words you have to decipher and type in to access a website – have been around since the 1990s. Their original purpose was to tell the difference between a human user and an automated system, by requiring the user to answer a challenge – one that was supposedly hard for […]

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SPF and TXT records and Go

A few days ago Laura noticed a bug in one of our in-house tools – it was sometimes marking an email as SPF Neutral when it should have been a valid SPF pass. I got around to debugging it today and traced it back to a bug in the Go standard library. A DNS TXT […]

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DNS Flag Day

There are quite a lot of broken DNS servers out there. I’m sure that’s no surprise to you, but some of them might be yours. And you might not notice that until your domains stop working early next year. DNS is quite an old protocol, and when it was originally specified there wasn’t really a […]

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Check your abuse addresses

Even if you have excellent policies and an effective, empowered enforcement team you can still have technical problems that can cause you to drop abuse mail, and so lose the opportunity to get a bad actor off your network before they damage your reputation further. It’s not quite as simple as “We’re seeing email in […]

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The Problem With Affiliates (2)

On Friday I mentioned spam coming from a BarkBox affiliate programme. The original email is here. It’s not terribly exciting, it’s rather typical spam of the sort sent by professional spammers. It’s validly DKIM and SPF authenticated, and DMARC-aligned. It includes invisible white-on-white padding text so that it doesn’t look like image-only spam to naive […]

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Reading RFCs

We mention RFCs quite a lot, both explicitly (RFC 6376 is the specification for DKIM) and implicitly (the 822.From aka bounce address aka return path). And we have local copies of a bunch of them to make them easy to refer to (SMTP, MIME, Carrier Pigeons …). They use quite a lot of jargon and […]

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