Content
# imap-mcp
A security-focused [Model Context Protocol][mcp] server that mediates LLM
access to IMAP mailboxes under strict, auditable policy. Designed for
agents that need to read, classify, move, and archive mail — but must be
prevented from reading what they shouldn't, moving what they shouldn't,
or leaving no trace of what they did.
[mcp]: https://modelcontextprotocol.io/
## Status
**V1 — 241 BDD scenarios green, 0 skipped.** The server is
runnable on stdio and HTTP/SSE transports. Gmail (with localized folder
name resolution via RFC 6154) and standard IMAP providers are supported.
Optional OpenTelemetry tracing with Jaeger.
## Quick start
```bash
# Install via pipx (recommended — isolated environment, global CLI)
pipx install "sc-imap-mcp[tracing]"
# Or via pip
pip install sc-imap-mcp[tracing]
# Without tracing
pipx install sc-imap-mcp
# From source
cd server && pip install -e ".[tracing]"
# Upgrade
pipx upgrade sc-imap-mcp
```
### Configure
```bash
mkdir -p ~/.config/imap-mcp/{policies,secrets/accounts/my-account}
# Create accounts.yaml, callers.yaml, policies/*.yaml
# (see Configuration section below)
# Store your IMAP password or OAuth refresh token
echo -n 'your-password' > ~/.config/imap-mcp/secrets/accounts/my-account/password
```
### Run on stdio (for Claude Desktop, Claude Code, Cline)
```bash
IMAP_MCP_CONFIG_DIR=~/.config/imap-mcp \
IMAP_MCP_CALLER_ID=my-agent \
imap-mcp --transport stdio
```
### Register with Claude Code
```bash
claude mcp add --scope user imap-mcp \
--env IMAP_MCP_CONFIG_DIR=$HOME/.config/imap-mcp \
--env IMAP_MCP_CALLER_ID=my-agent \
-- imap-mcp --transport stdio
```
### Run on HTTP (for multi-agent setups)
```bash
IMAP_MCP_CONFIG_DIR=~/.config/imap-mcp \
imap-mcp --transport http --host 127.0.0.1 --port 8080
```
## Architecture
```
┌──────────────────────────┐
│ LLM agent (MCP client) │
└────────────┬─────────────┘
│ MCP (stdio or HTTP/SSE)
┌────────────▼─────────────────────────────────────────┐
│ imap-mcp │
│ ┌─────────────────────────────────────────────────┐ │
│ │ Policy Decision Point — default-deny │ │
│ │ Redaction / Transparency Layer │ │
│ │ Transaction Manager (WAL + saga) │ │
│ │ IMAP Core · Batch Fetch · OAuth2 adapters │ │
│ │ Pluggable Secret Store │ │
│ │ Append-only Audit Log with hash chain │ │
│ │ OpenTelemetry Tracing (optional) │ │
│ └─────────────────────────────────────────────────┘ │
└─────────┬───────────────────┬────────────────────────┘
│ IMAP/IMAPS │ IMAP/IMAPS
┌─────────▼────┐ ┌──────────▼────┐
│ Account A │ │ Account B │
│ (e.g. Gmail) │ │ (e.g. Dovecot)│
└──────────────┘ └───────────────┘
```
## Configuration
The server reads its configuration from a directory of YAML files
pointed to by `IMAP_MCP_CONFIG_DIR`.
```
config/
├── accounts.yaml # IMAP accounts, secret store, audit, WAL
├── callers.yaml # MCP callers and their auth
└── policies/
├── invoice-agent.yaml
└── overview-bot.yaml
```
### accounts.yaml
Defines every IMAP account the server may connect to, plus the
secret store backend, audit log, and WAL configuration.
```yaml
accounts:
- id: company-mail
provider: imap-standard # or "google" for Gmail
host: imap.example.com
port: 993
auth:
type: password # or "xoauth2"
secret_ref: secret://accounts/company-mail/password
token_cache: memory_only # or "persist_all" (OAuth only)
- id: gmail-work
provider: google
host: imap.gmail.com
port: 993
auth:
type: xoauth2
secret_ref: secret://accounts/gmail-work/refresh_token
oauth_scope: https://mail.google.com/
token_cache: persist_all
- id: accounting@company.com
host: imap.company.com
port: 993
user: mail2223 # explicit IMAP login (when != id)
auth:
type: password
secret_ref: secret://accounts/accounting@company.com/password
secret_store:
backend: file_dir # or "env_var" or "gpg_file"
path: /home/user/.config/imap-mcp/secrets
audit:
directory: /home/user/.config/imap-mcp/audit
hot_days: 90 # days before gzip compression
warm_days: 275 # additional days as .gz
delete_after_days: 365 # total age before deletion
wal:
path: /home/user/.config/imap-mcp/wal.db
```
#### Account fields
| Field | Required | Default | Description |
|---|---|---|---|
| `id` | yes | — | Unique identifier referenced in policies. For Gmail with OAuth, use the email address (e.g. `user@company.com`) |
| `provider` | no | `imap-standard` | `imap-standard`, `google`, or `google-mock` |
| `host` | no | `127.0.0.1` | IMAP server hostname |
| `port` | no | `143` | IMAP port. Use `993` for IMAPS (Gmail, most providers) |
| `user` | no | derived from `id` | Explicit IMAP login username. Use when the IMAP user differs from the account id (e.g. `mail2223` for `accounting@example.com`) |
| `auth.type` | yes | — | `password` or `xoauth2` |
| `auth.secret_ref` | yes | — | Reference to the secret store (e.g. `secret://accounts/x/password`) |
| `auth.oauth_scope` | no | — | OAuth2 scope for xoauth2 accounts |
| `token_cache` | no | `memory_only` | `memory_only` (access tokens in RAM only) or `persist_all` (also persisted) |
#### Secret store backends
| Backend | Description | Config fields |
|---|---|---|
| `file_dir` | Plaintext files; confidentiality from the surrounding system (git-crypt, SOPS, LUKS) | `path` |
| `env_var` | Read-only from environment variables. | — |
| `gpg_file` | Per-file GPG decryption using the operator's key | `path`, `recipient`, `gnupghome` |
Secret references use the format `secret://path/segments`. For `file_dir`,
this resolves to `{path}/path/segments`.
### callers.yaml
Defines every MCP caller (agent) that may connect to the server.
```yaml
callers:
- id: my-agent
policy: my-policy
auth:
type: stdio_trusted
- id: invoice-bot
policy: invoice-policy
auth:
type: shared_token
token_secret_ref: secret://callers/invoice-bot/token
```
#### Caller auth types
| Type | Transport | Mechanism |
|---|---|---|
| `stdio_trusted` | stdio only | Caller ID set via `IMAP_MCP_CALLER_ID` env var by the orchestrator. |
| `shared_token` | stdio + HTTP | Bearer token verified with constant-time comparison. On HTTP: `Authorization: Bearer <token>` header. |
Caller identity is immutable for the session duration. No impersonation
primitive exists.
### policies/\<name\>.yaml
Each policy file defines what one caller may see and do.
```yaml
name: my-policy
accounts:
company-mail:
- path: INBOX
mode: blacklist
default: ENVELOPE
mark_seen: true
rules: []
gmail-work:
- path: INBOX
mode: whitelist
default: NONE
mark_seen: true
move_out: true
rules:
- match: { from_domain: hornbach.de }
grant: FULL
- match: { from_domain: amazon.de }
grant: FULL
- path: Archive
mode: whitelist
default: NONE
accept_incoming: true
rules: []
```
#### Folder policy fields
| Field | Required | Default | Description |
|---|---|---|---|
| `path` | yes | — | IMAP folder path (e.g. `INBOX`, `INBOX/Invoices`, `[Gmail]/All Mail`) |
| `mode` | yes | — | `whitelist` (default=NONE, rules grant access) or `blacklist` (default>NONE, rules cap access) |
| `default` | yes | — | Default visibility level when no rule matches |
| `rules` | no | `[]` | Sender-specific overrides (see below) |
| `mark_seen` | no | `false` | Can toggle `\Seen` flag |
| `mark_tagged` | no | `false` | Can set keywords and `\Flagged` |
| `move_out` | no | `false` | Can remove messages from this folder |
| `accept_incoming` | no | `false` | Can receive messages moved/copied in |
| `draft_append` | no | `false` | Can append new drafts |
#### Visibility levels
Each rule grants exactly one level from this hierarchy:
```
NONE < COUNT < METADATA < ENVELOPE < HEADERS < BODY < FULL
```
| Level | What is exposed |
|---|---|
| `NONE` | Nothing (message is invisible) |
| `COUNT` | Message count only (`folder_stats`) |
| `METADATA` | UIDs, sizes, flags (`search`) |
| `ENVELOPE` | From, To, Subject, Date (`fetch_envelope`, `list_messages`) |
| `HEADERS` | Full RFC 5322 header block (`fetch_headers`) |
| `BODY` | Plain-text and HTML bodies (`fetch_body`) |
| `FULL` | Everything including attachments (`fetch_attachment`) |
#### Sender rule grammar
Rules use a closed set of predicates. Predicates within one rule are
AND-combined; multiple rules in a folder are OR-combined.
| Predicate | Type | Example |
|---|---|---|
| `from` | exact email | `alice@example.com` |
| `from_domain` | domain (case-insensitive, trailing-dot tolerant) | `hornbach.de` |
| `to` | exact email | `billing@company.com` |
| `to_contains` | substring | `team` |
| `subject_contains` | substring (case-insensitive, NFC-normalized) | `rechnung` |
| `has_attachment` | boolean | `true` |
| `flagged` | boolean | `true` |
| `newer_than` | duration | `30d` |
| `older_than` | duration | `90d` |
| `size_gt` | bytes | `10000` |
| `size_lt` | bytes | `1500` |
In `whitelist` mode, rules use `grant: <level>`. In `blacklist` mode,
rules use `cap: <level>`. Mixing both in one folder is a parse-time
error.
The `flagged` predicate matches the IMAP `\Flagged` flag (starred in
Gmail), enabling rules like "grant full access to all starred messages":
```yaml
- path: INBOX
mode: whitelist
default: NONE
rules:
- match: { flagged: true }
grant: FULL
```
## MCP tool surface
Nineteen tools, each gated on exactly one visibility level or one
capability.
### Read tools (10)
| Tool | Min visibility | Description |
|---|---|---|
| `list_accounts` | — | List visible accounts + `hidden_accounts_count` |
| `list_folders` | COUNT | List visible folders + `hidden_folders_count` |
| `list_labels` | COUNT | Gmail only: list labels with flags |
| `list_messages` | ENVELOPE | **Primary tool for reading mail.** Returns from, subject, date per message. Supports criteria and pagination. |
| `folder_stats` | COUNT | Message counts per visibility level |
| `search` | METADATA | Search for UIDs with `matched_total` / `matched_visible` / `filtered_out` |
| `fetch_envelope` | ENVELOPE | From, To, Subject, Date for a single message by UID |
| `fetch_headers` | HEADERS | Full RFC 5322 headers |
| `fetch_body` | BODY | Plain-text and HTML bodies |
| `fetch_attachment` | FULL | MIME attachment bytes |
### Write tools (6)
| Tool | Required capability | Description |
|---|---|---|
| `mark_seen` | `mark_seen` | Toggle `\Seen` flag on a single message |
| `bulk_mark_seen` | `mark_seen` | Toggle `\Seen` on all messages matching criteria |
| `mark_tagged` | `mark_tagged` | Add/remove keywords |
| `move` | `move_out` + `accept_incoming` | Move message (intra-account: native MOVE; cross-account: saga) |
| `copy` | `accept_incoming` | Copy message to target folder |
| `create_draft` | `draft_append` | Append RFC 5322 draft |
### Meta tools (3)
| Tool | Description |
|---|---|
| `describe_policy` | Caller's own policy profile (accounts, folders, capabilities, hidden counts). Never reveals rule patterns or other callers. |
| `get_caller_identity` | Resolved `caller_id` for the current session |
| `get_transaction_status` | WAL state of a cross-account move saga |
### Deliberately absent
`delete`, `expunge`, `raw_imap_command`, `fetch_raw_rfc822`, cross-account
search, MCP resource subscriptions, folder CRUD, policy reload via MCP.
See [ADR 0018](docs/adr/0018-non-goal-tool-surface.md).
## Environment variables
| Variable | Required | Description |
|---|---|---|
| `IMAP_MCP_CONFIG_DIR` | yes | Path to the configuration directory |
| `IMAP_MCP_CALLER_ID` | stdio_trusted only | Caller identity for stdio transport |
| `IMAP_MCP_OAUTH_CLIENT_ID` | xoauth2 accounts | OAuth2 client ID from GCP Console |
| `IMAP_MCP_OAUTH_CLIENT_SECRET` | xoauth2 accounts | OAuth2 client secret from GCP Console |
| `IMAP_MCP_HTTP_HOST` | no | Bind address for HTTP (default: `127.0.0.1`) |
| `IMAP_MCP_HTTP_PORT` | no | Port for HTTP (default: `0` = ephemeral) |
| `IMAP_MCP_APPEND_TIMEOUT` | no | Timeout in seconds for IMAP APPEND |
| `OTEL_EXPORTER_OTLP_ENDPOINT` | no | OTLP endpoint for tracing (e.g. `http://localhost:4317`) |
## OAuth2 bootstrap
For accounts with `auth.type: xoauth2` (e.g. Gmail), run the
interactive bootstrap once per account to obtain the refresh token:
```bash
IMAP_MCP_CONFIG_DIR=~/.config/imap-mcp \
IMAP_MCP_OAUTH_CLIENT_ID=your-client-id.apps.googleusercontent.com \
IMAP_MCP_OAUTH_CLIENT_SECRET=your-client-secret \
imap-mcp-oauth-bootstrap --account user@company.com
```
This prints a URL. Open it in a browser, complete the Google consent
flow, then paste the redirect URL back into the terminal. On success,
the refresh token is stored in the secret store. The server then
exchanges it for access tokens automatically.
### Setting up a GCP OAuth client
1. Go to https://console.cloud.google.com/apis/credentials
2. Create credentials > OAuth client ID > Desktop app
3. Copy the Client ID and Client Secret
4. Use them as `IMAP_MCP_OAUTH_CLIENT_ID` and `IMAP_MCP_OAUTH_CLIENT_SECRET`
## Tracing (optional)
Install with tracing support and start Jaeger:
```bash
pip install sc-imap-mcp[tracing]
cd ops/tracing && docker compose up -d
# Add to your MCP server config:
OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4317
```
Open http://localhost:16686 for the Jaeger UI. Every MCP tool call
creates a trace with nested IMAP connection and authentication spans.
## Policy reload
Send `SIGHUP` to the running server process. The server re-parses the
entire config directory, validates it, and swaps the in-memory state
atomically. Parse or validation errors preserve the previous policy
and write an audit record with the error.
```bash
kill -HUP $(pidof imap-mcp)
```
## Gmail support
Accounts with `provider: google` get explicit Gmail semantics:
- `list_labels` tool available (Gmail only)
- `search` results include `canonical_all_mail_uid` for cross-label deduplication
- Intra-account `move` implemented as label swap (not physical MOVE)
- Cross-account sagas fetch deterministically from `[Gmail]/All Mail`
- `[Gmail]/Trash`, `[Gmail]/Drafts` etc. are policy-addressable folders
- Localized folder names (e.g. `[Gmail]/Entwürfe` in German) are
resolved to canonical paths via RFC 6154 special-use flags
## Audit log
Append-only JSONL with SHA-256 hash chain, one file per UTC day.
Strict no-content-leak rule: no message bodies, subjects, attachment
filenames, OAuth tokens, or cleartext sender addresses in DENY records.
## Implementation stack
- **Language:** Python 3.11+
- **IMAP:** `aioimaplib` (IMAP4 and IMAP4_SSL)
- **MCP:** the official `mcp` SDK (stdio + HTTP/SSE)
- **Storage:** `aiosqlite` for WAL; YAML for config
- **Validation:** `pydantic` v2 (strict mode)
- **OAuth:** `httpx` + first-party flow implementation
- **Tracing:** OpenTelemetry (optional, via `[tracing]` extra)
- **Testing:** `pytest` (property tests) + `behave` (BDD, 241 scenarios)
## Testing
```bash
# BDD suite (requires Docker for IMAP fixtures)
cd bdd && docker compose -f docker/docker-compose.yml up -d
.venv/bin/behave --no-color --format=progress features/
# Server property tests
cd server && .venv/bin/pytest tests/policy/ -q
```
## Documentation
The design is captured in 23 ADRs under [`docs/adr/`](docs/adr/).
Limitation records under [`docs/limitations/`](docs/limitations/).
Error-path analysis at
[`docs/error_path_analysis.md`](docs/error_path_analysis.md).
## License
GPL-3.0-or-later. See [`LICENSE`](LICENSE).
MCP Config
Below is the configuration for this MCP Server. You can copy it directly to Cursor or other MCP clients.
mcp.json
Connection Info
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