# a2a-mailbox (mcpb · a2a-mailbox.mcpb)

Cross-CLI agent mailbox: tmux-injected messaging for Claude Code, Codex, Pi and ZCode

- Trust score: 39/100 (low)
- Registry status: active
- Liveness: live
- Owner verified: no
- Last scored: 2026-11-06

## Components

- mcpb · `a2a-mailbox.mcpb`: 39/100 (this document), [markdown](https://verifymcp.io/servers/regretsss-a2a-mailbox/a2a-mailbox.md), [page](https://verifymcp.io/servers/regretsss-a2a-mailbox/a2a-mailbox)

## Channel facts

- Registry: `mcpb`
- Package: `https://github.com/RegretSSS/a2a-mailbox/releases/download/v0.1.0/a2a-mailbox.mcpb`
- Transport: `stdio`
- SHA-256: `3635d09a48c2669f1af8c0d0e32a48b5414099ed162997b6ab35fc956c3f8d5a`

## Trust breakdown

How this component scores in each security and reliability category. Every signal is checked automatically from public evidence about the published package, including repeated runs of it in an isolated sandbox, and we only credit what we can confirm. Scores are 0–100 per category. Scoring method: https://verifymcp.io/docs/scoring (what has changed: https://verifymcp.io/docs/scoring/changelog)

Scored 2026-11-06.

- **Supply Chain Security**: 12/100
  - No malware scan is available for this kind of package: the supply-chain vendors we use do not cover it. This is a permanent gap in our coverage, not a finding about the package.
  - Known CVEs were checked across the 15 of 15 dependencies we could resolve, so this covers what we could see, not the whole tree.
  - Install-script risk not yet assessed.
  - 1 of 15 dependencies flagged as unhealthy.
- **Provenance & Transparency**: 45/100
  - Source repository is publicly reachable at the declared URL.
  - Provenance check failed: no build-provenance attestation is published.
  - Clear OSI-approved license (Apache-2.0).
  - Actively maintained (last published 0 days ago).
  - Disclosure check failed: no security disclosure policy was found in the source repository.
- **Schema Quality & AI Usability**: 67/100
  - AI-judged instruction clarity (good).
  - Tool/resource definitions use about 404 tokens (~67/item across 6 items; 6 tools + 0 resources), lean.
  - Usage-examples check failed: none of the tools include examples.
- **Stability & Change Management**: 0/100
  - Stability not yet verified: not enough scan history yet (needs a 30-day window).
- **Tool Coverage**: 71/100
  - 100% of tools have a non-trivial description (not blank, and not just the tool's name).
  - 0% of tool parameters carry a description.
  - Structured output schemas are declared (100% of tools); any adoption earns full credit.
- **Tool Safety**: 75/100
  - No prompt-injection markers were found in the server instructions, tool names or descriptions we captured.
  - 0 of 1 tool(s) whose name or description implies an irreversible operation declare an MCP destructiveHint annotation; "mail_send" implies "send" and declares no destructiveHint at all, which the MCP spec reads as destructive by default.
  - An AI judge read all 6 captured unit(s) of tool text and found none that tries to manipulate the model reading it.
- **Capabilities**: 100/100
  - Implements a current MCP spec version (2026-07-28).

**Unverified: 1 category.** A category scored 0 because we could not verify it: a data source with nothing on this package, evidence we could not reach, or a check we could not run. We only credit what we can confirm.

## Install

### How do I install the a2a-mailbox MCP server?

a2a-mailbox ships as an MCPB bundle, a single file you download and open in an MCP host that supports MCPB bundles, such as Claude Desktop. The host reads the launch command from the bundle's own manifest, so there is no command to copy. Before opening it, check the file's SHA-256 matches the one the MCP registry declares for it, 3635d09a48c2669f1af8c0d0e32a48b5414099ed162997b6ab35fc956c3f8d5a; the commands to do that are on this page. If it does not match, do not open it.

- Download bundle: `https://github.com/RegretSSS/a2a-mailbox/releases/download/v0.1.0/a2a-mailbox.mcpb`
- SHA-256: `3635d09a48c2669f1af8c0d0e32a48b5414099ed162997b6ab35fc956c3f8d5a`

### Verify on macOS / Linux

```bash
echo "3635d09a48c2669f1af8c0d0e32a48b5414099ed162997b6ab35fc956c3f8d5a  a2a-mailbox.mcpb" | shasum -a 256 -c
```

### Verify on Windows (PowerShell)

```powershell
(Get-FileHash -Algorithm SHA256 .\a2a-mailbox.mcpb).Hash -eq "3635d09a48c2669f1af8c0d0e32a48b5414099ed162997b6ab35fc956c3f8d5a"
```

## Changelog

Every change recorded for this component, newest first. Days that predate change tracking, or that we cannot explain, say so: "we were watching and nothing happened" and "we were not watching" are different claims.

### 2026-11-05 (score 39)

First indexed and scored.

## MCP tools (6)

### `mail_send` (~84 tokens)

Mail Send

发消息给另一 agent。in_reply_to 用 mail_read 返回的 msg_id（可自动确认原消息）；expect_reply=True 唤醒词尾加『[需回函]』。

Input parameters:

- `body` (string, required)
- `context` (string)
- `expect_reply` (boolean)
- `in_reply_to`
- `to` (string, required)

Output parameters:

- `result` (string)

### `mail_poll` (~26 tokens)

Mail Poll

列出自己邮箱待处理消息的摘要（不消费，可反复查）。

Output parameters:

- `result` (string)

### `mail_read` (~33 tokens)

Mail Read

读自己邮箱一条消息全文（含 ack_id——业务确认用）。

Input parameters:

- `msg_id` (string, required)

Output parameters:

- `result` (string)

### `mail_ack` (~52 tokens)

Mail Ack

确认一条消息（幂等）。ack_id 用 mail_read 返回的；跨主机传输不可见时自证落盘 self_attested。

Input parameters:

- `ack_id` (string, required)

Output parameters:

- `result` (string)

### `mail_who` (~72 tokens)

Mail Who

列出在册 agent（默认只列在线 active，含同目录分身行 agent_id@session短码 可定向发信；all=true 附已下线 stale）。group-only 标记与成员计数，附联邦 peers 状态。

Input parameters:

- `all` (boolean)

Output parameters:

- `result` (string)

### `mail_group` (~137 tokens)

Mail Group

群组权限五合一。action=join 申请加入对方 group(agent_id=门主,note=来意)；action=pending 列自己的待审申请；action=admit 批准 agent_id 可发给自己；action=revoke 移出 agent_id；action=gate 开关仅准入名单收件闸(group_only=true 开,group 为展示名)。错误返回含完整用法。

Input parameters:

- `action` (string, required)
- `agent_id` (string)
- `group` (string)
- `group_only` (boolean)
- `note` (string)

Output parameters:

- `result` (string)

## Diagnostics

Captured diagnostic sections: Provenance, Dependencies. The full working is on the page: https://verifymcp.io/servers/regretsss-a2a-mailbox/a2a-mailbox#diagnostics

## Score history

- 2026-11-06: 39
- 2026-11-05: 39

## Common questions

### What is the a2a-mailbox MCP server?

a2a-mailbox is an MCP server listed in the public MCP registry as io.github.RegretSSS/a2a-mailbox. Cross-CLI agent mailbox: tmux-injected messaging for Claude Code, Codex, Pi and ZCode. This page covers its MCPB bundle (https://github.com/RegretSSS/a2a-mailbox/releases/download/v0.1.0/a2a-mailbox.mcpb).

### Is the a2a-mailbox MCP server safe to use?

a2a-mailbox scores 39 out of 100 on VerifyMCP. That is a record of what we were able to check automatically, not an endorsement. The category breakdown on this page shows every signal behind the number, including the ones we could not confirm.

### What tools does the a2a-mailbox MCP server expose?

a2a-mailbox exposes 6 tools: mail_send, mail_poll, mail_read, mail_ack, mail_who, mail_group. Their descriptions and schemas cost roughly 404 tokens of context every time the server is loaded.

### What licence is the a2a-mailbox MCP server under?

a2a-mailbox declares the Apache-2.0 licence, which is OSI-approved. That covers the source only, and says nothing about the cost of any service it calls.

### What did VerifyMCP test on the a2a-mailbox MCP server?

VerifyMCP ran 13 checks on a2a-mailbox, covering Known CVEs, Dependency health, Source repository, Provenance and 9 more. 3 items could not be completed, a gap on our side rather than a finding about a2a-mailbox: Malware scan, Install scripts and Stability. One category scores 0 for that reason, because we only credit what we can confirm. Endpoint Security and Transport & Reachability do not apply to an MCPB bundle, so they were not tested. The score does not measure everything, and the scoring documentation lists what it leaves out.

## Links

- Repository: https://github.com/RegretSSS/a2a-mailbox
- Changelog RSS feed: https://verifymcp.io/servers/regretsss-a2a-mailbox/a2a-mailbox.xml
- Changelog JSON feed: https://verifymcp.io/servers/regretsss-a2a-mailbox/a2a-mailbox/changelog.json
- Trust report (JSON): https://verifymcp.io/servers/regretsss-a2a-mailbox/a2a-mailbox.json
- HTML version of this page: https://verifymcp.io/servers/regretsss-a2a-mailbox/a2a-mailbox