Cold email in 2026: what indie hackers got wrong (with a Python validator I built to enforce the new rules)

If you've been sending B2B cold emails the same way for 18 months, your reply rate just dropped to ~0% and you don't know why. I rebuilt my outreach this week after my reply rate tanked from 4% to Autobound , MarketingProfs , HyperGen , Instantly ), built a Python validator to enforce the new rules across 70+ template files in my repo, and shipped 10 trimmed emails that comply. Here's what changed and the SOP for fixing your stack. What changed in 2026 1. DMARC is now hard-rejected. In Feb 2024,