CategoryTechnical

3 weeks ago

Diagnosing Hard Bounces

By steve
2 Min read
Add comment
28January

A very short post about diagnosing hard bounces, because I’ve had to give the same advice to a dozen folks over the past few months. When you’re diagnosing and mitigating hard bounce rates the first thing you’ll see is your ESPs dashboard or reporting. It’ll tell you how many emails you sent bounced, and how that number has changed over time. A useful start. But a hard...

2 months ago

Tracking link maths

By steve
3 Min read
3 comments
10December

How long does a tracking link need to be? Let’s make it interesting, and say we want to be able to have a unique tracking link for every single atom in the observable universe. That’s about 1080 unique links. One hundred novemdecillion exa-links. 100,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 If we have that many customers...

3 months ago

There’s text and then there’s text

By steve
8 Min read
2 comments
28November

If you want to send someone an email with some text in it there are quite a few different ways you can do it. The main differences are the ways the text is packaged up in MIME entities to be sent. text/plain This is the simplest sort of text you can send. If you send a simple email with many desktop mail clients, this is what you get. You can’t include images, you can’t choose fonts...

3 months ago

Your bounce classification is a bit rubbish

By steve
3 Min read
1 comment
26November

When a mailbox provider rejects or defers an email it sends back a message explaining why. Those messages begin with a three digit number (starting with a “5” for rejections and a “4” for deferrals), followed by text that explains why the mail wasn’t accepted. That text often contains a link to follow for more information, or a mailbox provider specific code you can...

3 months ago

Comparing DKIM keys

By steve
3 Min read
2 comments
20November

Sometimes we have a client who has done something wrong when setting up authentication. Their DKIM signing fails due to something being wrong with the public key they’ve published. The published key looks fine, by eye. It’s got all the fields it should have, but diagnostic tools give inscrutable error messages. If you’re lucky, “This doesn’t seem to be a valid RSA...

6 months ago

DNS Failures

By steve
5 Min read
2 comments
28August

We use DNS a lot in email, particularly for authentication, so diagnosing why DNS isn’t returning what we expect it to is a pretty common challenge. And DNS responses aren’t exactly the clearest thing to understand. There are two types of DNS server we need to know about. When we publish DNS records for our own domain we add them to a nameserver that is authoritative for our domain...

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