The verifier returned (True, 'mx_unreachable') when it couldn't complete a port-25
probe to ANY MX — marking 438,163 addresses email_verified=TRUE. But these are NOT
dead: they're dominated by Comcast (13.7k), AT&T/SBCGlobal (13.5k), Verizon, Cox,
Charter, Frontier, etc. — major ISPs that deliberately tarpit/refuse probes from
unknown IPs. Confirmed from prod: comcast MX connects + returns 220. The probe
failure ≠ undeliverable.
Fix: return (False, 'mx_probe_blocked') — MX exists, deliverability UNKNOWN, must
be confirmed by a real send. Excluded from PW campaigns; prime burner-verification
target (burner_list_verify upgrades it to send_confirmed on delivery). Existing
438,163 mx_unreachable rows reclassified in prod to mx_probe_blocked / verified=FALSE.
1eb29f80be