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AuthenticationResend and React Email
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Platform and application verification/password-reset messages render the repository's React Email templates. Both Resend and SMTP send HTML plus a plain-text link. These are authentication messages, not a bulk mail or operational-alert service.
Set these server-only values before starting the API:
QB_MAIL_PROVIDER=resend
QB_RESEND_API_KEY=replace_with_provider_api_key
QB_MAIL_FROM=QB Flex <hello@example.com>Use a sender authorized by your provider and test verification/reset on your deployment. Keep the API key out of browser VITE_* configuration, Studio screenshots and source control. Templates live in packages/auth/src/email/templates.tsx; there is no Studio template editor yet.
| Setting | Behavior |
|---|---|
QB_MAIL_PROVIDER=resend | Requires QB_RESEND_API_KEY; explicitly chooses Resend. |
QB_MAIL_PROVIDER=smtp | Uses the SMTP relay even when a Resend key is present. |
QB_MAIL_PROVIDER=auto or omitted | Chooses Resend when its key exists, otherwise SMTP. |
SMTP is an alternative adapter, not automatic failover after a failed Resend send. Delivery errors are surfaced; configuration presence or a provider's acceptance does not prove inbox delivery.
QB_MAIL_PROVIDER=smtp
QB_SMTP_HOST=127.0.0.1
QB_SMTP_PORT=7615
QB_SMTP_SECURE=false
QB_MAIL_FROM=QB Flex <hello@localhost>These host/port values are for native development with Compose Mailpit. Containers use mailpit:1025. Set QB_SMTP_USER and QB_SMTP_PASSWORD only if the relay requires authentication. QB_SMTP_SECURE=true selects implicit TLS; configure the port to match your relay. Mailpit's local inbox is http://localhost:7616.
Production requires the selected provider's configuration. Never assume production mail works because local Mailpit passed. Enable project verification settings and use allowlisted callback URLs. See application authentication and Deployment Doctor for lifecycle and redacted inventory checks.