Our best-converting email had no subject line.

We A/B tested subject lines for a re-engagement email to 40,000 dormant users.

Control: "We miss you — here's what's new"
Variant A: "3 things you missed"
Variant B: "Your account is still here"
Variant C: no subject line (blank)

Open rates:
Control: 18%
Variant A: 21%
Variant B: 24%
Variant C: 31%

The blank subject line won by a wide margin. In inboxes, it rendered as "(no subject)" — which looked like a personal email, not a marketing one. Click-through was also highest for the blank version, and unsubscribe rate was lowest.

We could not scale it. A blank subject line works once, as an anomaly. Sending every email with no subject would train users to ignore it, or worse, look like spam. But it taught us something we had forgotten: our emails looked like emails from a company, and users had learned to skip those.

What would your email look like if it were trying to be read, not just sent?