# Production Email Architecture & Delivery State Model

**Document Version:** 1.0.0 (Phase 21)

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## 1. Delivery State Model

LeadPilot accurately reflects delivery transport status without making false claims:
- `queued`: Enqueued for background worker dispatch.
- `sent`: Accepted by SMTP relay server.
- `failed`: Provider rejected dispatch or connection failed.

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## 2. Retry Classification

- **Transient / Retryable Errors:** Connection timeouts, rate limits (HTTP 429, SMTP 421/450/451/452), server 5xx errors.
- **Permanent / Non-Retryable Errors:** 550 User Unknown / Mailbox Not Found, 535 Authentication Failed, 501 Syntax Error.

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## 3. Lead State Isolation

Transport delivery failures do **not** change lead status to `Lost`. Transport state is kept strictly independent from commercial sales outcomes.