jwz-go

jwz-go

jwz-go is a pure-Go implementation of Jamie Zawinski's mail-threading algorithm — the same threading model that ships in Mozilla Thunderbird and most modern MUAs.

Given a flat slice of email headers, jwz.Build returns a slice of Thread trees, joining messages by Message-ID / In-Reply-To / References, with a locale-aware subject-match fallback for orphans.

Features

  • Pure Go, zero dependencies. Drop in to any mail client, archive viewer, or mailing-list tool without dragging anything else along.
  • Deterministic output. Threads sort newest-first by LatestAt with a stable EmailID tiebreaker; children sort by Date. The same input produces byte-identical trees every run.
  • Locale-aware subject fallback. Groups orphan messages whose references were stripped by intermediate MTAs across Re:, Fwd:, AW:, WG:, SV:, RV:, Odp:, Antw:, ENC:, and more.
  • Loop-safe. Cycle detection in link() prevents pathological reply chains from blowing the stack.
  • Application-defined IDs. Carry your own row/UID through the tree via EmailID — no extra lookup needed when rendering.
Note

This library is only the threading algorithm. It does not parse RFC 5322 mail, fetch IMAP, or sanitize HTML. You bring the headers; it returns the trees.