Complete Secure Newsletter Admin Feature

I need an experienced developer to complete a newsletter feature inside the existing admin dashboard of my live real estate website.

The application uses Replit, React/TypeScript, Express, PostgreSQL and Resend. Existing code and documentation are available for review; the feature is not yet fully tested or ready for production.

The work includes reviewing the existing implementation, completing consent and email confirmation, unsubscribe and suppression, campaign preview and approval, secure admin access, and protection against duplicate sending. Testing must use an independent environment with synthetic data and mock emails.

Please provide your relevant experience, a quote and timeline by stage, including any infrastructure costs. No changes to the live website, database, credentials or permissions, no deployment and no real emails without my separate approval.