Substack now lets you test two (or more) subject lines, and after just an hour, it picks the winner and sends that one to the rest of your audience.
I’m as excited as
is:
As a Substack bestseller, I have access to the beta testing.
So today’s A/B testing session was packed with so many golden nuggets based on my tests and my 15+ years as a professional marketing and brand manager.
If you’ve ever stared at your email subject line and wondered, “Is this actually going to get opened?” — this one’s for you.
Because here’s the truth:
Half of your subscribers decide to open (or not!) based on a few tiny words in their inbox.
And now with Apple Intelligence (aka iOS 18.2) changing how inboxes work — sorting emails into Primary, Promotions, Updates, or even Spam — you’re not just writing for humans anymore. You’re writing for bots too.*
*We’ll dig into this in our Google and AI Bootcamp with the #1 authority when it comes to Google Knowledge Panels. Interested? Let me know in the comments! Annual members will get a fantatsic discount.
Here’s what we covered in today’s data-driven session:
✅ Why your subject line is also your headline — and how that simple shift can change everything.
✅ How to use Substack’s new A/B title test feature (and pitfalls to avoid).
✅ What not to do
✅ How long your subject line should be based on data
✅ What works, e.g. power words
✅ How Apple’s AI buckets your emails — and which trigger words help you land in the Primary tab.
✅ The exact tools I use to test my own subject lines — 3 and one winner
We also talked about the exact tools I use to test my own subject lines — including the one I started using back in summer 2024 that helped me push my open rates by 15%. Crazy, right?
💎BONUS: Also, I share a smart AI prompt that helps you analyze your subject lines and predict the winner like a pro.
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