Experiment 001, deliverability
We rebuilt our setup three times. The problem was one checkbox.
Most of the people on our lists use Microsoft. When our emails did not land there, we blamed the infrastructure. Three times.
Three setups, three failures
On our last list, 59% of recipients were on Microsoft. So Microsoft was the inbox that mattered.
| Setup | What happened | Verdict |
|---|---|---|
| Google inboxes sending to Microsoft | Replies were thin | Failed |
| Real Outlook inboxes, warmed like Google | 7,357 emails over seven months, 2 real replies | Failed |
| Azure: one domain, 50 inboxes, tiny volume each | 490 people, 1 reply: an out of office | Failed |
The clue
Then seven of our sending domains were listed on a blocklist in the same week. One of them had never sent a single campaign. We still do not know what caused those listings, and we do not blame them on what comes next. But it changed the question: not what is wrong with each setup, but what do all our emails have in common?
The discovery
We sent a real campaign email to our own Outlook inbox. It went to junk. So we opened the raw source.
There is an unsubscribe header in every email. You do not see a button, but the link is in the code. That link is not on our domain. It sits on a shared domain the sending platform uses for every customer, and it was the only link in the whole email.
The paired test
Same day, same inbox, within two hours:
| Header | Result | |
|---|---|---|
| Campaign email to Outlook | On | Junk |
| Same email to Gmail | On | Inbox |
| Campaign email to Outlook | Off | Inbox |
| Plain two line email to Outlook | On | Junk |
| Different sending domain to Outlook | On | Junk |
SPF, DKIM and DMARC passed on every one. All passing.
What we do now
We turned the header off. The opt out is now one plain line at the bottom of the email: if this is not relevant, reply “no” and we will not follow up. No link, no unsubscribe page.
To be clear: that is four emails into one inbox. It is not a study. It is one result from one setup, and it changed how we send. On a different list, a campaign with the header on still got replies from Microsoft users. Test it on your own sends before you change anything.
Try this
Send one of your real campaign emails to your own Outlook inbox. Open the raw source and search for List-Unsubscribe. If the link in it is not on your own domain, you have the same question we had.
Want this for your outbound?