Experiment 006, infrastructure
A bounce on email two means something else.
If we had watched one number, we would have known a domain was dying 15 weeks earlier. You probably already have that number: your bounces, split by which email bounced.
How bounces usually get read
The common advice is to keep your bounce rate under 2%. Mostly it is used to judge the email verifier, and for email one that makes sense. The bounces on email two and three tell you something very different.
What we found in our old setup
While building our own domain health check, we went back through our old infrastructure. One domain bounced a few times more than its siblings. The interesting part was when: about 40% of its bounces came on email two and three, not email one.
Why the step matters
| The bounce | What it means | Whose problem |
|---|---|---|
| On email one | The address is probably bad | Your list |
| On email two or later, after the address took email one | The address was fine a few days ago. The server started rejecting you | Your domain |
Looking back, that signal was there 15 weeks before the domain was finished. Fifteen weeks of time and money on a domain that was already dying.
It works the other way too
Around the same time, our deliverability tool labelled two of our sending domains as burned. We checked their bounces on email two and later: zero. So we did not retire them because of a label. Both were retired later, on other signals: one for a Spamhaus listing (see 003), the other because it got no replies of any kind, not even an out of office, while its siblings did. The label alone was never the reason.
To be clear: a few bounces mean nothing. You need enough of them, and you compare a domain with its siblings in the same campaign, not with a fixed number.
Try this
Take your bounces and split them by which email they bounced on. If one domain has a lot more bounces on email two and later than its siblings, that domain is being rejected.