toinbox/simplerelay ? reverse-engineered prompt

Build me a self hosted SMTP relay app with a web dashboard that lets me send email through different upstream SMTP providers depending on the sender address.

I want users to be able to register, log in, add providers, test their SMTP settings, check DNS setup like SPF, DKIM, and DMARC, and send a test email. The relay should keep a log of sent, failed, and bounced messages, show basic stats on the dashboard, and let me search through mail history.

Please also include admin tools for managing users, changing roles, turning accounts on or off, setting relay limits and expiry, and viewing overall system health. It should support per sender access control so only allowed IPs can use each provider, with optional SMTP auth as an extra layer. Make it safe so it cannot become an open relay.

If useful, look up current docs online for any setup details, and make it easy to run with Docker.