feat: add inbound forward rule tools and thread search

[mklocek]

Adds MCP tools for an inbox's forward rules and a search option on the threads list. forwards on messages and delivery on sent thread messages come through in the existing message and thread output.

Changes

• list-inbound-forward-rules, get-inbound-forward-rule, create-inbound-forward-rule, update-inbound-forward-rule and delete-inbound-forward-rule
• search on list-inbound-threads, combinable with last_id
• README, manifest.json and CLAUDE.md list the new tools

Summary by CodeRabbit

• New Features
  • Added tools to list, retrieve, create, update, and delete inbox forwarding rules, with configurable conditions and destinations.
  • Added optional search when listing inbound email threads. Search matches subjects and sender, recipient, CC, and BCC addresses, and can be reused when paging through results.
  • Forward-rule updates can change selected fields; supplied conditions or destinations replace the full set, and an empty array clears it.

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📒 Files selected for processing (2)

• README.md
• src/server.ts

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📝 Walkthrough

📝 Walkthrough

Walkthrough

Inbound thread listing now accepts an optional search filter. The pull request also adds tools to list, retrieve, create, update, and delete inbound forward rules.

Changes

Inbound thread search

Layer / File(s)	Summary
Thread search filtering src/tools/inbound/schemas/listInboundThreads.ts, src/tools/inbound/listInboundThreads.ts, src/tools/inbound/__tests__/listInboundThreads.test.ts, src/server.ts, README.md, CLAUDE.md	The thread-list schema and tool accept optional search text. The handler passes it to the API, includes it in empty-result messages, and tells callers to reuse it when paginating. Documentation describes the case-insensitive matching fields.

Inbound forward-rule management

Layer / File(s)	Summary
Forward-rule schemas src/tools/inbound/schemas/forwardRuleFields.ts, src/tools/inbound/schemas/*InboundForwardRule.ts	Adds validation schemas for rule conditions, destinations, and inputs to list, get, create, update, and delete operations.
Forward-rule operations and tests src/tools/inbound/*InboundForwardRule.ts, src/tools/inbound/__tests__/*InboundForwardRule.test.ts	Adds handlers for the five operations. Tests cover validation, API calls, returned results, and API errors.
Tool registration and documentation src/server.ts, src/tools/inbound/index.ts, manifest.json, README.md	Registers and exports the tools and adds manifest and README descriptions. Updates modify only supplied fields; supplied condition or destination arrays replace the full sets.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant Caller
  participant MCPServer
  participant listInboundForwardRules
  participant MailtrapAPI
  Caller->>MCPServer: Call a registered forward-rule tool
  MCPServer->>listInboundForwardRules: Pass tool input
  listInboundForwardRules->>MailtrapAPI: Validate input and request rule operation
  MailtrapAPI-->>listInboundForwardRules: Return operation result or error
  listInboundForwardRules-->>Caller: Return formatted tool response

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Merge Risk: 🔵 Low · up to 1fc24

Malformed forwarding conditions can pass local validation and reach the API. This is a bounded validation risk; the reported SDK compatibility concerns do not remain.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 1fc24

The new tools can change where future inbound email is copied. They retain the existing credential model, but forwarding-condition validation does not enforce all documented restrictions. Remote authorization and mutation guarantees remain unverified; no unauthorized forwarding or data disclosure was established.

Retained concerns

• Low · security · observed: The new forwarding contract documents required predicate values, required header names, and header-only operators, but neither JSON Schema nor runtime validation enforces those relationships. Create and update send accepted malformed combinations directly to the API. Because these predicates determine which messages are forwarded, fail-closed interpretation depends on remote behavior that was not established; this is not evidence that the API accepts malformed rules or discloses email.

Security review details

Security Blast Radius

• inferred — A caller able to invoke the new tools can request forwarding changes for caller-selected inboxes and destinations using the server's configured credential. Potential exposure extends to future matching email in every inbox that credential is permitted to manage, rather than only the messages returned by one read call. Cross-account access or authority beyond that credential's permissions was not established.

Trust Boundaries and Controls

• observed — The handlers require MAILTRAP_API_TOKEN but do not require MAILTRAP_ACCOUNT_ID. This matches existing inbound deletion behavior and does not remove a previous credential check. Local code validates input structure, then delegates resource authorization to the remote API; token-to-inbox and rule ownership enforcement was not verified.

Resilience and Maintainability Implications

• inferred — A transport failure after a remote commit could leave the tool caller uncertain whether forwarding changed. The local error response does not establish that prior routing remains intact or that replay is safe. This is a recovery uncertainty relevant to persistent email-routing controls, not an observed partial update or duplicate rule.

Hardening Proposals

• proposed — Enforce the documented cross-field predicate restrictions in both advertised and runtime schemas. For unattended callers, consider explicit approval or destination restrictions for match-all forwarding changes; these would be additional safeguards, not fixes for a demonstrated authorization bypass.

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Pre-merge checks | 3 | 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Description check		The description identifies the main changes and lists the new tools, but it omits the required Motivation and How to test sections. It also does not provide the Images and GIFs section from the templa…	Add a Motivation section, document the test commands or test cases in How to test, and include the Images and GIFs section or state that images are not applicable.
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 7 functions across 21 files. (1 skipped: 1…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check		The title clearly summarizes the two primary changes: inbound forward-rule tools and thread search.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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Full details: Description check

Explanation

The description identifies the main changes and lists the new tools, but it omits the required Motivation and How to test sections. It also does not provide the Images and GIFs section from the template.

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Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 7 functions across 21 files. (1 skipped: 1 unsupported.)

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Actionable comments posted: 3

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @src/tools/inbound/listInboundForwardRules.ts:
- Line 28: Update package.json and the lockfile to a mailtrap SDK release that
provides inbound.forwardRules, then verify createInboundForwardRule and
updateInboundForwardRule pass params matching the SDK’s create and update types.
In src/tools/inbound/listInboundForwardRules.ts lines 28–28, the call and its
inferred callback types should resolve through the SDK upgrade; no direct change
is needed. In src/tools/inbound/createInboundForwardRule.ts lines 28–28, ensure
params match the SDK create type. In src/tools/inbound/getInboundForwardRule.ts
lines 28–28, no direct change is needed. In
src/tools/inbound/updateInboundForwardRule.ts lines 32–32, ensure params match
the SDK update type. In src/tools/inbound/deleteInboundForwardRule.ts lines
28–28, no direct change is needed.

Review comments at @src/tools/inbound/listInboundThreads.ts:
- Line 30: Update the SDK dependency used by listInboundThreads so
threads.getList transmits the search parameter, and expose search only with that
supported released version. Ensure the same SDK update supports the forward-rule
tools that depend on it.

Review comments at @src/tools/inbound/schemas/forwardRuleFields.ts:
- Around line 67-74: Add a superRefine to conditionZod to enforce the condition
field dependencies: require value except for empty and not_empty operators,
require header_key for header match_type, and allow empty/not_empty only with
header. Report actionable validation issues on the relevant fields so invalid
conditions are rejected before reaching the API.

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📥 Commits

Reviewing files that changed from the base of the PR and between 6272835 and 8d2a86a.

📒 Files selected for processing (24)

• CLAUDE.md
• README.md
• manifest.json
• src/server.ts
• src/tools/inbound/__tests__/createInboundForwardRule.test.ts
• src/tools/inbound/__tests__/deleteInboundForwardRule.test.ts
• src/tools/inbound/__tests__/getInboundForwardRule.test.ts
• src/tools/inbound/__tests__/listInboundForwardRules.test.ts
• src/tools/inbound/__tests__/listInboundThreads.test.ts
• src/tools/inbound/__tests__/updateInboundForwardRule.test.ts
• src/tools/inbound/createInboundForwardRule.ts
• src/tools/inbound/deleteInboundForwardRule.ts
• src/tools/inbound/getInboundForwardRule.ts
• src/tools/inbound/index.ts
• src/tools/inbound/listInboundForwardRules.ts
• src/tools/inbound/listInboundThreads.ts
• src/tools/inbound/schemas/createInboundForwardRule.ts
• src/tools/inbound/schemas/deleteInboundForwardRule.ts
• src/tools/inbound/schemas/forwardRuleFields.ts
• src/tools/inbound/schemas/getInboundForwardRule.ts
• src/tools/inbound/schemas/listInboundForwardRules.ts
• src/tools/inbound/schemas/listInboundThreads.ts
• src/tools/inbound/schemas/updateInboundForwardRule.ts
• src/tools/inbound/updateInboundForwardRule.ts

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[mklocek]

ping @leonid-shevtsov