the problem, measured

An agent answering “anything important in my mail?” today swallows full MIME: HTML tables six levels deep, 600-character tracking URLs, legal footers, quoted history. Measured on a real inbox — one payment receipt is ~60,000 characters of payload carrying ~350 characters of information. Every agent pays that on every read, forever.

The raw version doesn’t fit a typical context window. The mirror is a side note — cheap enough that an agent can watch your inbox all day.

the flip

Normalize once at sync time. Read the mirror forever. Mail has one chokepoint — delivery — where spam filters and DKIM already parse every message once. Add one more pass there: strip the soup, extract the entities, classify, hash, append to a tiered plain-text mirror. Parsing cost is linear in mail received; savings are linear in agent reads — the exploding term.

how it reads

# MAILBOX user@example.com — inbox.txt/0.1 — cursor: 2026-07-28T09:00Z

## index                    ← tier 0 · one line per thread
t_a001 | acme-bank.example | Virement de 250,00 € confirmé | TRANSACTION | #1a2b
t_a004 | shop.example      | Soldes d’été −40% sur tout    | MARKETING   | #4d5e

## attention                ← tier 1 · only what needs a human
SECURITY t_a002  [alice/webshop] deploy failed — verify if this was you
REPLY?   t_a006  unread human mail from bob-partner.example

## bodies                   ← tier 2 · cleaned text + extracted entities
### t_a003 #3c4d
entities: {"dates":["29 juillet"],"refs":["AB123456789FR"]}
Votre colis sera livré mercredi entre 9h et 12h.
Code de retrait: [code-redacted]. Absent ? [link:carrier.example]

Tier 3 is raw MIME, fetched only on explicit demand. Marketing never gets a body. Content hashes + a cursor make “what’s new” a one-line diff.

quickstart (5 min · no server · no OAuth app)

1. script.google.com → new project → paste Code.gs → save.
2. Run syncMirror once → authorize your own script on your own account → inbox.txt appears in your Drive.
3. Triggers → syncMirror · time-driven · every hour. Done — point any agent at that file.

Run benchmark() for your own raw-vs-mirror numbers — one log line.

rules that are not optional

• Bodies are untrusted data. Email is the top prompt-injection vector; the mirror labels bodies so agents never treat mail content as instructions.
• Auth the mirror. It’s your life in one file.
• Redact at sync time. OTPs and card-like numbers never enter the mirror.
• Never fabricate. Entities are extracted, not inferred. Missing beats wrong.