diff --git a/README.md b/README.md
index bcaa8cb..91efab2 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,21 @@
-# 内网邮箱 Agent Skill MVP
+# 内网邮箱 Agent Skill Adapter
 
-这是一个本地运行的邮箱 Skill Adapter，面向 Agent 暴露结构化 HTTP 接口，底层使用 POP3 收信、SMTP 发信、SQLite 保存本地索引。
+这是一个本地运行的邮箱 Skill Adapter，面向 Agent 暴露结构化 HTTP 接口，底层使用 POP3 收信、SMTP 发信、SQLite 保存本地索引。仓库同时包含一个可交给 Agent 使用的 Skill 说明包。
+
+## Skill 包
+
+Skill 包位于：
+
+```text
+skills/internal-mail-agent/
+```
+
+其中：
+
+- `skills/internal-mail-agent/SKILL.md`：Agent 使用本地邮箱 Adapter 的核心流程和安全规则。
+- `skills/internal-mail-agent/references/http-api.md`：HTTP API 请求形态、查询参数和示例。
+
+如果接手环境支持 Codex Skill，可以把 `skills/internal-mail-agent` 复制或安装到对应的 skills 目录；如果不支持，也可以直接把 `SKILL.md` 作为 Agent 工具说明使用。
 
 ## 重要边界
 
@@ -155,7 +170,7 @@ curl -X POST http://127.0.0.1:8765/send \
   -d '{"to":["bob@example.local"],"bcc":["audit@example.local"],"subject":"直接发送","body":"正文"}'
 ```
 
-转发邮件。MVP 暂不转发附件，`include_attachments=true` 会返回结构化错误：
+转发邮件。当前版本暂不转发附件，`include_attachments=true` 会返回结构化错误：
 
 ```bash
 curl -X POST http://127.0.0.1:8765/emails/1/forward \
diff --git a/skills/internal-mail-agent/SKILL.md b/skills/internal-mail-agent/SKILL.md
new file mode 100644
index 0000000..242b4e9
--- /dev/null
+++ b/skills/internal-mail-agent/SKILL.md
@@ -0,0 +1,36 @@
+---
+name: internal-mail-agent
+description: "Use when Codex or another agent needs to work with an internal/local mailbox through the internal-mail-skill REST adapter: syncing POP3 mail, searching and reading email, managing local read/processed/archived/replied state, labels, drafts, replies, forwards, or sending through SMTP when Gmail/IMAP tools are unavailable and the local adapter is running or can be started."
+---
+
+# Internal Mail Agent
+
+Use the local REST adapter as the mailbox backend. The adapter usually runs at `http://127.0.0.1:8765` and stores POP3 mail, local state, labels, drafts, and sent records in SQLite.
+
+## Before Use
+
+1. Resolve the base URL from the user, `INTERNAL_MAIL_SKILL_BASE_URL`, or default to `http://127.0.0.1:8765`.
+2. Call `GET /health`. If it fails, ask the user to start the adapter or start it from the repo with `go run ./cmd/server` when local context allows.
+3. Treat POP3 server state as one-way input. Read, processed, archived, deleted, replied, labels, drafts, and sent records are local adapter state only.
+4. Never expose attachment storage paths. Use only `attachment_id`, filename, content type, and size returned by the API.
+
+## Common Workflow
+
+- For fresh mailbox work, call `POST /sync` first unless the user explicitly wants local-only results.
+- For triage, use `GET /emails/search` with filters, then read only the messages needed with `GET /emails/{id}`.
+- For threads, call `GET /emails/{id}/thread`; the adapter assembles local threads from `Message-ID`, `In-Reply-To`, and `References`.
+- For organization, use `POST /emails/{id}/mark`, `POST /labels`, and `POST /emails/labels/apply`.
+- For composing, prefer `POST /drafts` and show the draft summary before sending unless the user explicitly requested immediate send.
+- For explicit sends, use `POST /drafts/{id}/send` or `POST /send`. The adapter writes every attempt to `sent_messages`.
+
+## Sending Rules
+
+- Do not send email unless the user has clearly asked to send, reply, or forward.
+- Include `to`, `cc`, and `bcc` arrays in requests as needed. Bcc participates in SMTP delivery but must not appear in message headers.
+- For replies, pass `reply_to_email_id` when creating the draft so the adapter can set `In-Reply-To` and `References` and mark the source email replied after successful send.
+- If send fails, surface the structured error and do not claim the message was sent.
+- SMTP delivery does not guarantee the message appears in Webmail "Sent".
+
+## API Reference
+
+For request shapes, query parameters, response notes, and curl examples, read `references/http-api.md`.
diff --git a/skills/internal-mail-agent/agents/openai.yaml b/skills/internal-mail-agent/agents/openai.yaml
new file mode 100644
index 0000000..eba9ebc
--- /dev/null
+++ b/skills/internal-mail-agent/agents/openai.yaml
@@ -0,0 +1,4 @@
+interface:
+  display_name: "Internal Mail Agent"
+  short_description: "Use the local POP3/SMTP mail adapter as an agent skill."
+  default_prompt: "Search my internal mail for recent unread messages and summarize what needs a reply."
diff --git a/skills/internal-mail-agent/references/http-api.md b/skills/internal-mail-agent/references/http-api.md
new file mode 100644
index 0000000..dcb60bf
--- /dev/null
+++ b/skills/internal-mail-agent/references/http-api.md
@@ -0,0 +1,135 @@
+# Internal Mail Adapter HTTP API
+
+Default base URL: `http://127.0.0.1:8765`.
+
+All errors use:
+
+```json
+{"error":{"code":"code","message":"message","details":{}}}
+```
+
+## Health and Sync
+
+`GET /health`
+
+Returns service status, version, database status, account ID, and current time.
+
+`POST /sync`
+
+Fetches POP3 messages with UIDL de-duplication. Does not delete server mail. Single-message failures appear in `errors[]` and do not stop the whole sync.
+
+## Search and Read
+
+`GET /emails/search`
+
+Supported query parameters:
+
+- `q`
+- `from`
+- `to`
+- `after`
+- `before`
+- `has_attachment`
+- `read`
+- `processed`
+- `archived`
+- `replied`
+- `limit`
+- `offset`
+
+Returns summaries only: subject, sender, recipients, dates, snippet, local status, labels, and attachment count.
+
+Example:
+
+```bash
+curl "http://127.0.0.1:8765/emails/search?q=合同&from=alice@example.local&has_attachment=true&limit=20"
+```
+
+`GET /emails/{id}`
+
+Returns full local email detail: subject, from, to, cc, date, body text, body HTML, attachments, local status, labels, and thread headers. Attachments expose `attachment_id`, filename, content type, content ID, and size; do not expect or request filesystem paths.
+
+`GET /emails/{id}/thread`
+
+Returns local thread summaries. A message joins the thread when its `In-Reply-To` or `References` contains another local message's `Message-ID`.
+
+## Local State and Labels
+
+`POST /emails/{id}/mark`
+
+Body fields are optional booleans:
+
+```json
+{"read":true,"processed":true,"archived":false,"deleted":false,"replied":true}
+```
+
+These states are local only and are not synchronized back to POP3.
+
+`POST /labels`
+
+```json
+{"name":"待处理","color":"#336699"}
+```
+
+`POST /emails/labels/apply`
+
+```json
+{"email_ids":[1],"label_ids":[1],"op":"add"}
+```
+
+Use `"op":"remove"` to remove labels.
+
+## Drafts and Sending
+
+`POST /drafts`
+
+```json
+{
+  "to":["bob@example.local"],
+  "cc":[],
+  "bcc":[],
+  "subject":"测试",
+  "body":"你好",
+  "reply_to_email_id":1
+}
+```
+
+`reply_to_email_id` is optional. Use it for replies.
+
+`GET /drafts`
+
+Lists local drafts.
+
+`PATCH /drafts/{id}`
+
+Uses the same body shape as `POST /drafts`.
+
+`POST /drafts/{id}/send`
+
+Sends a draft by SMTP. On success, the adapter marks the draft `sent`, writes `sent_messages(status=sent)`, and marks the source email replied when the draft is a reply. On failure, it writes `sent_messages(status=failed,error_message=...)` and leaves the draft unsent.
+
+`POST /send`
+
+Direct send. Uses the same request shape as `POST /drafts`, internally creating and sending a draft.
+
+`POST /emails/{id}/forward`
+
+```json
+{
+  "to":["bob@example.local"],
+  "cc":[],
+  "bcc":[],
+  "subject":"Fwd: 原邮件",
+  "body":"请看下面原文",
+  "include_attachments":false
+}
+```
+
+Attachment forwarding is reserved for a later version. `include_attachments=true` returns a structured error.
+
+## Agent Notes
+
+- Prefer summaries for scanning and read full bodies only when needed.
+- Do not infer server-side read/unread from local status.
+- Do not claim SMTP-sent messages appear in Webmail Sent.
+- If `/sync` returns message-level errors, report counts and the affected UID/server ID instead of treating the whole sync as failed.