Email prototype — Duplicate detection and automated-mail suppression

Detail 2 of 3 from the same offline Python email prototype, built with AI assistance using synthetic messages. SQLite records processed messages by Message-ID, with a SHA-256 fallback when no ID exists. The first run created 2 drafts, 5 review items and 1 ignored automated message. Repeating the same 8 inputs with the same database produced 8 duplicates and no new drafts.

Header checks also suppress automated and bulk mail. This is exact-key detection, not semantic deduplication or a live mailbox integration. No paid client deployment; no email is sent.

Full prototype: https://contra.com/p/3bLEO7OF-offline-email-workflow-prototype-with-python