Postbuch — Correspondence Register
YEAR
2026
MY ROLE
Design, development, deployment and production migration
INDUSTRY
Nonprofit
STACK USED
- FastAPI
- PostgreSQL
- Tesseract OCR
- IMAP
- MinIO (S3)
- OIDC
- Alembic
- Caddy
- Docker Compose
Project Overview
German associations and public bodies keep a Postbuch: a register of every official letter they send or receive, who handled it and how it was resolved. It is usually a paper ledger or a spreadsheet nobody updates. This one fills itself in: email arrives over IMAP, scanned letters are OCR'd into searchable text, and every change is recorded with what it was before and after.
I built the application, the mail-import worker and the storage path, and wrote the runbooks for setup, backup and the production migration. It runs from a clone with one command and fictional demo correspondence.
Key Features
Two ways in
A dedicated scanner mailbox turns every attachment into a register entry.
A normal shared inbox goes to triage, where a person decides what belongs in the register.
Searchable paper
Tesseract reads scans in German and English, and skips documents that already carry text.
Built for accountability
Every change records who made it and a before/after diff.
New categories go through a proposal and approval step, so the taxonomy doesn't sprawl.
Project Gallery
Challenges Solved
One bad mailbox stopping all imports
Each import cycle is isolated, so an unreachable mailbox, a malformed message or a failed OCR run is logged and skipped. Failed imports are stored with their status, so they show up in the interface rather than only in a log file.
A developer login reaching production
The instant developer login needs two settings at once — enabled and not production — so copying the wrong configuration file can't switch it on in production.
Going live without starting empty
The production migration restores the development database, then removes test users, test mailboxes and audit history while keeping the scanned correspondence worth archiving.
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