📄 Article
✓ Link checked
Free
Beginner
Why we picked it This is the actual data behind one of the rules founders lean on: Boomerang analyzed over 300,000 emails and found all-caps subject lines get replies roughly 30 percent less often, partly because spam filters flag them. If you want proof rather than just a rule to trust, this is the two-minute read that gives it to you.
The One Thing You Should Never Do In An Email Subject (Based on Data)
From Boomerang by Brendan G.
- All-caps subject lines get replies about 30 percent less often than normal-case ones (34.6% vs 50.0% in this dataset).
- Spam detection systems specifically flag all-caps subjects, hurting deliverability before a human ever sees it.
- Urgency-signaling tricks like this often backfire against the very goal they are meant to serve.
