$ man stop-optimizing

Stop Optimizing What Doesn't Matter Yet

The anti-pattern of optimizing second-order variables (send time, subject line length, emoji usage, signature format) before first-order variables (infrastructure, data quality, deliverability) are solid. Premature optimization for email.

If your emails aren't landing in the inbox, it doesn't matter what time you send them. If your data is 30% invalid, it doesn't matter how good your subject line is. If your domains aren't warmed, it doesn't matter how personalized your icebreakers are. First-order variables (deliverability, data quality, infrastructure) determine whether your email gets seen. Second-order variables (copy, timing, personalization) determine whether it gets replied to. Fix them in order.

When a partner asks about send time optimization or subject line testing, I check the fundamentals first. Is deliverability healthy? Is the bounce rate low? Is the data clean? Are domains warmed? If yes to all — great, let's optimize copy and timing. If no to any — we're not optimizing copy yet. We're fixing infrastructure. I've seen teams obsess over A/B testing subject lines while 40% of their emails land in spam. The subject line isn't the problem. The fundamentals are.