simplelogin-mcp

An HTTP MCP server exposing the alias endpoints of the SimpleLogin API, gated by a configurable permission level.

Quick start

docker run -p 8000:8000 \
  -e SIMPLELOGIN_API_KEY=your-api-key \
  -e SIMPLELOGIN_PERMISSION_LEVEL=read \
  ghcr.io/samanthavbarron/simplelogin-mcp:latest

The MCP endpoint is served at /mcp over streamable HTTP; /health answers liveness probes.

Related MCP server: mailpouch

Configuration

An unrecognised permission level is rejected at startup rather than defaulted, so a typo cannot silently grant a level you did not intend.

Permission levels

Levels are cumulative — each includes those below it.

Enforcement happens at two independent layers: tools above the configured level are omitted from tools/list, and refused by the call handler. A client that hard-codes or guesses a hidden tool name gains nothing, and the refusal happens before any request reaches SimpleLogin.

Why delete grants nothing

Alias deletion is not exposed. Deleting an alias is irreversible and permanently reserves the address, which is a poor trade in an agent-driven context. Use toggle_alias to disable an alias instead — it stops mail forwarding and is reversible.

DELETE /api/aliases/:id was the only destructive endpoint in scope, so no tool currently requires the delete level. The level remains defined so configuration stays forward-compatible, and the test suite asserts that it grants nothing beyond update. The underlying HTTP client has no delete method at all, and tests verify that no operation at any level issues a DELETE upstream.

Tool notes

• Pagination. List tools accept an optional 0-based page_id. Supply it to fetch one page (20 items); omit it to auto-paginate up to SIMPLELOGIN_MAX_AUTO_PAGES. Responses carry has_more, so truncation is always visible.

• Creating a custom alias needs a signed_suffix from get_alias_options and mailbox_ids from list_mailboxes. The suffix is cryptographically signed and cannot be constructed by hand.

• list_mailboxes is a read-only addition outside the alias endpoint set, included because alias creation is unusable without it.

• Contacts are premium-gated. create_alias_contact returns SimpleLogin's upgrade message on free accounts.

• Blocking one sender is toggle_contact_block, not toggle_alias. It flips a single contact's block_forward, leaving the alias working for everyone else. Identify the contact by its address or by its reverse-alias address (both appear in mail headers), or by contact_id. The contact is always resolved against the supplied alias_id, so an id belonging to a different alias is refused rather than acted on.

Parameter shapes are gateway-driven

Two conventions look odd in isolation and exist for a concrete reason. Some MCP gateways — LiteLLM's among them — validate arguments against the published schema before forwarding, while passing values through as strings. A union like int | None renders as anyOf: [integer, null], which a string satisfies neither branch of, so such parameters are rejected outright.

• page_id is a plain integer using -1 as the "auto-paginate" sentinel.

• pinned and disable_pgp are the string enum "true" / "false" / "unchanged", since string branches survive intact.

• mailbox_ids is a plain list where empty means unchanged.

Optional string parameters are unaffected and remain str | None. tests/test_tool_schemas.py enforces that no parameter is ever a union without a string branch.

Development

uv sync --locked --dev
uv run pytest -m "not image and not live"   # offline: no network, no container
uv run pytest -m "image and not live"       # against the built container image
uv run pytest -m live                       # against the real SimpleLogin API

Offline tests run against a stateful in-memory fake modelled on real captured API responses, so they need neither credentials nor network access.

Live tests

Live tests need SI_API_TEST_KEY and run the built image against the real service. They are shaped around two measured constraints:

• Alias creation is heavily rate limited. An exhausted window was observed still refusing after six minutes idle, while reads, PATCH and toggle were unaffected. The suite therefore shares one durable fixture alias across runs and only creates in the two tests that specifically exercise creation. Those skip rather than fail when throttled.

• The account is shared and small. Everything ephemeral is stamped with the run id and removed in a finally block. Only stamped aliases are ever deleted, so the account's own aliases are never at risk. Teardown uses a direct API client, never the server under test.

Deletion in the test harness is intentional and lives only there — see tests/e2e/live_harness.py.

CI

• Offline tests run on every push and pull request, including from forks.

• Image E2E builds and exercises the container on native amd64 and arm64 runners.

• Live E2E is currently limited to manual workflow_dispatch runs while the shared test account is throttled on alias creation, so it cannot block publishing. Trigger it by hand to check whether the throttle has lifted; see the comment in .github/workflows/ci.yml for how to re-enable automatic runs. When enabled it runs only where secrets are available (forked pull requests skip it) and is serialised by a concurrency group, since all runs share one account. pull_request_target is deliberately not used — it would expose secrets to untrusted contributor code.

• Images publish to GHCR as latest and sha-<short>, built per-architecture on native runners and merged into one manifest.

License

MIT