As a consumer there are several different sorts of email address that are described as “disposable” or “temporary”. Some of them are what we might call tagged addresses – addresses that are unique, created to be given to a specific vendor. If it’s misused by the vendor, or if it’s leaked to spammers, then the address can be disabled, either by rejecting...
Trekkie Monster. He’s obsessed by social media and isn’t owned by Children’s Television Workshop. What is a Cookie? I’m not talking about biscuits, nor about web cookies, at least not exactly. When you’re talking to a protocol developer a cookie is a thing you’re given, that you hang on to for a while, then give back. If you leave your suitcase with your hotel...
Seen this recently? 451 Message temporarily deferred due to unresolvable RFC.5321 from domain; see This is Yahoo doing some extra work to identify that the 5321.From domain1The return-path, aka the 821.From, 5321.From, or bounce address is the email address you send from at the protocol level, not the email address in the From: header, and it’s the address any bounces will be sent to. of...
Several times recently I’ve heard about something unusual happening email delivery-wise at academic domains that was new, and wasn’t being seen at non-academic domains on the same lists. Most recently it was aggressive following of all links in an email at delivery time, seen at several .edu domains, all using the same mail provider. Not that unusual a thing in itself, we know that...
When we’re looking at the technical details of email addresses there are two quite different contexts we talk about. One is an “821 address” or “5321 address”. This is the email address as it’s used by the SMTP protocol, as part of the “MAIL FROM: <>” or “RCPT TO: <>” commands sent to the mailserver. It’s defined in RFC 821...
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...
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
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.
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...
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...
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