A/B test the subject lines across two cohorts of 50 mid-market leads each (hold body, preview text, and send window constant). Keep preview text under 90 characters and aligned with the subject's verb so the inbox snippet reads as one thought — the current audience treats mis-aligned previews as spam. Avoid trigger words ("free", "guaranteed", all-caps blocks); warm sends use the same POLSIA_API_KEY proxy as Email 1, so domain reputation is shared — soft-launch the test on verified (mx/pattern/api) rows first, then expand once opens stay flat.