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Don’t break the (RFC) rules

It looks like Microsoft are getting pickier about email address syntax, rejecting mail that uses illegal address formats. That might be what’s causing that “550 5.6.0 CAT.InvalidContent.Exception: DataSourceOperationException, proxyAddress: prefix not supported – ; cannot handle content of message” rejection. Why do we care? It’s good to send syntactically valid...

Life of an Email

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

Gmail Program for Election Mail

A few months ago, Google made a splash in the political press and the email marketing space when they asked the FEC the following question: May Google launch a free and non-partisan pilot program to test Gmail design features, which will be open to authorized candidate committees, political party committees, and leadership political action committees, where spam detection as applied to messages...

Confidential to ESPs

Dear Colleagues at ESPs, We have a problem. More specifically, YOU have a problem. You have a spam problem. One that you’re not taking care of in any way, shape or form. There was a point where ESPs started caring about spam out of their networks. They got blocked enough they had to take action. Because they took action a lot of the big blocklists started being nice. Spamhaus, for instance...

When best practices don’t work

I started out with the best intentions to get back into the swing of things with blogging more regularly. But between MAAWG recovery, COVID recovery and life it’s not worked out that way. This is an excerpt of something I wrote over on slack to explain why someone was still struggling with delivery even though best practices weren’t working. Hope it will be helpful for some folks...

Sending email

I did a class at M3AAWG teaching the basic mechanics of sending an email, both really by hand using dig and netcat, and using SWAKS. No slides, but if you’re interested in the script I’ve posted a very rough copy of my working notes here.

The gang is trickling in

It’s been a few years since we’ve actually made it to a MAAWG. We missed much of 2018 and 2019 due to our international move. Then 2020 San Francisco conflicted with a personal engagement. Then, well, pandemic hit and it’s been virtual and then we were moving and … wow, it’s been busy! We did make it to London, though, and have started reconnecting with colleagues...

ESPs need to step up their compliance game

I don’t send a lot of spam complaints generally. Mostly I block and move on. There are some companies, though, that I offer the professional courtesy of sending a complaint or a report to their abuse@ address. Former clients, friends and colleagues generally get that courtesy. The number of ESPs that completely fail to take any action is disappointing. Too many of them can’t even...

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...

Message not compliant with the RFCs

Every once in a while we’ll see a rejection from Yahoo that says RFCs 554 5.0.0 Message not accepted due to failed RFC compliance. What does that mean and what can we do about it? It really does mean exactly what it says on the label: there’s something about the message that is not in compliance with any number of RFCs and are not going to accept the message in its current state. When...

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