Outbound SMTP ports are often blocked on VPS; EMAIL_TRANSPORT=http_api sends via Resend HTTPS (Brevo optional). OpenSMTPd/SMTP remain available.
Job process_reminders in subscription_worker; REMINDER_LEAD_HOURS window; CalenTIQ email + in-app event_reminder; idempotent reminder_sent. Refs EventHub/EventHubBack#70