references/protocol.md — Mail and Files Connector

From version 0.1.0 of Mail and Files Connector, shown publicly by its creator. 2.1 KiB · SHA-256 20787a971fe318c9e5c59863f4bb3bfe5678374d63543685ae6370300fd26028.

# Protocol and result bounds

Each JSON-RPC 2.0 message occupies one line. The current 2026-07-28 style carries `_meta` keys `io.modelcontextprotocol/protocolVersion` and `io.modelcontextprotocol/clientCapabilities` in every request. `server/discover` reports `supportedVersions`, capabilities, and server information in `_meta`; its complete result and `tools/list` include `resultType: complete`, `ttlMs: 0`, and `cacheScope: private`. Modern `tools/call` results have `resultType: complete` and no caching hints. Legacy 2025-11-25 and 2025-06-18 clients can use `initialize` and `notifications/initialized`. Unsupported versions receive error -32022 with every supported version and the requested version in `data`.

List tools return at most 50 items and identify skipped additional pages. Oversized metadata is truncated and Graph download URLs are omitted, with an incomplete marker. An incomplete tool result includes `incomplete` and `skipped` and sets `isError: true`; starting the server with `--allow-partial` sets `isError: false` for those results. Partial results never change the process exit status. `mail_read` returns at most 10,000 body characters. Graph JSON is returned as JSON in tool content and structured content; callers must treat it as untrusted data. Version 0.1.0 has no write tools. No delivery or write-verification feature is present.

The server reads the complete Graph JSON response (at most 2,000,000 bytes) before applying item and body output limits; a 50-item or body limit does not restrict upstream reads. No additional pages are fetched. Stdin is read as bytes, with a 1,000,000-byte line limit including its newline; larger lines receive a clear error and are drained in bounded byte chunks. Strict UTF-8 decoding occurs per request: undecodable lines receive JSON-RPC -32700 and serving continues. JSON output escapes non-ASCII characters so stdout works in UTF-8 and C locales. Test fixtures are read once with a 2,000,000-byte limit; malformed JSON, fixture entries, collection items, pagination metadata and message bodies are rejected explicitly.

By Zero Width Lab (zerowidthlab.com)

License: MIT (read it).

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