CategoryTechnical

Stop with the incorrect SPF advice

Another day, another ESP telling a client to publish a SPF include for the wrong domain. It shouldn’t annoy me, really. It’s mostly harmless and it’s just an extra DNS look up for most companies. Heck, we followed Mailchimp’s advice and added their include to our bare root domain and it’s not really a huge deal for companies with only a couple SaaS providers. Still...

Command Line Tools

Tools that you run from the command line – i.e. from a terminal or shell window – are often more powerful and quicker to use than their GUI or web equivalents. Their output is plain text so it’s much easier to copy and paste into an email or a slack conversation – sure, you can take a screenshot of a GUI tool and share that, but then the folks you’re sharing it with...

Apple MPP reporting and geolocation

A while back I wrote about Apple Mail Privacy Protection, what it does and how it works. Since MPP was first announced I’d assumed that it would be built on the same infrastructure as iCloud Private Relay, Apple’s VPN product, but hadn’t seen anything from Apple to explicitly connect the two and didn’t have access to enough data to confirm it independently. But the nice...

Apple MPP

You’ve probably heard about Apple Mail Privacy Protection. Email marketing chat has been all a-twitter about it since it was announced in June. Skipping over all the “Openpocalypse” panic, what is it and what does it do? Image Loads It’s all about images in email and how they’re loaded (particularly invisible one pixel images that are used solely for tracking). Why...

The OSI Seven Layer Model

In the 1970s, while the early drafts of the Internet were being developed, a competing model for networking was being put together by the ISO (International Organization for Standardization). The OSI (Open Systems Interconnection) Model broke the work needed to implement a distributed network service into seven separate layers of abstraction, from the physical infrastructure at layer one all the...

Authentication

Some notes on some of the different protocols used for authentication and authentication-adjacent things in email. Some of this is oral history, and some of it may be contradicted by later or more public historical revision. SPF Associates an email with a domain that takes responsibility for it. Originally Sender Permitted From, now Sender Policy Framework. It allows a domain owner to announce...

Link tracking redirectors 2

It’s not too difficult to build your own link redirector, perhaps a few hours work for a basic implementationme, 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 dedicated click-tracking webserver, mostly as a demo of how to use...

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 the email, their web browser fetches the link from the...

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 and wait for people to complain you can use the DMARC policy “pct=” tag to roll...

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 sends another command. The main exception to that is when the client sends the payload of the email. Once the server...

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