Outlook COM MCP Server

Microsoft Graph APIを利用できないWindows環境で、Classic Outlookのメールと予定表をMCPクライアントから扱うためのローカルMCPサーバーです。

A local Model Context Protocol (MCP) server for reading Classic Outlook mail and calendar data and creating reply drafts through COM, without Microsoft Graph API.

できること

メールを検索し、選択したメッセージの本文を取得する
予定表のイベントを取得する
返信または全員返信をOutlookの下書きへ保存する
選択したメールを明示的に既読または未読へ変更する

送信、削除、移動、アーカイブは行いません。対象はWindows上のClassic Outlookで、現在は初期開発段階です。

Warning

このプロジェクトは、現在サインインしているClassic Outlookプロファイルのデータを読み取ります。MCPクライアントがツールを呼び出すと、選択したメールまたは予定表データがそのクライアントへ返されます。利用前に、所属組織のデータ取扱規定を確認してください。

This project reads data from the currently signed-in Classic Outlook profile. When an MCP client calls a tool, the selected mail or calendar data is returned to that client. Confirm your organization's data-handling policy before use.

Why this exists

Some environments cannot use Microsoft Graph because app registration, tenant consent, or Graph permissions are unavailable. This server uses the Outlook desktop COM object model as a local alternative.

It is deliberately narrow:

Read mail metadata and selected message bodies.
Read calendar events.
Enumerate Inbox, Sent, or Drafts folder trees and search nested folders.
Save a reply or reply-all message to Outlook Drafts.
Explicitly mark one selected message as read or unread.
Never send, delete, move, or archive messages.

Status

Early development. The server targets Windows and Classic Outlook only. New Outlook for Windows does not support COM automation.

Architecture

        MCP client
             |
             | stdio (JSON-RPC)
             v
      OutlookComMcp.exe
             |
             | dedicated STA thread + COM late binding
             v
        Classic Outlook

The implementation uses late-bound COM instead of redistributing Outlook interop assemblies. Outlook calls run on one dedicated single-threaded apartment (STA) thread.

MCP tools

Tool	Effect	Notes
`search_emails`	Read-only	Searches Inbox, Sent, Drafts, or a supplied folder. Supports recursive and unread-only searches. Body previews are opt-in.
`list_mail_folders`	Read-only	Lists a mail folder tree and returns folder/store IDs for targeted searches.
`get_email`	Read-only	Reads one message using the `EmailId` and `StoreId` returned by search.
`set_email_read_state`	State change	Explicitly marks one selected message as read or unread. Search and read tools never change this state.
`list_calendar_events`	Read-only	Lists events overlapping an ISO 8601 range of up to 31 days.
`create_reply_draft`	Additive write	Saves a reply draft. It does not send mail. Reply-all must be explicitly requested.

Tool results use structured content and bounded result sizes. Email bodies are untrusted input and must not be interpreted as instructions.

Requirements

Windows 10 or later
Classic Outlook for Windows, installed and configured
An interactive Windows session for the same user whose Outlook profile is accessed
.NET 8 SDK to build, or .NET 8 Desktop Runtime for a framework-dependent release

The server is not intended to run as LocalSystem, a Windows service, or a headless server process.

Build

dotnet restore OutlookComMcp.sln
dotnet build OutlookComMcp.sln --configuration Release
dotnet test OutlookComMcp.sln --configuration Release

Publish a framework-dependent Windows executable:

dotnet publish src/OutlookComMcp/OutlookComMcp.csproj `
  --configuration Release `
  --runtime win-x64 `
  --self-contained false `
  --output artifacts/win-x64

Run over stdio

The server writes MCP protocol messages to stdout. Diagnostics go to stderr.

dotnet run --project src/OutlookComMcp/OutlookComMcp.csproj

Example configuration for a local stdio-capable MCP client:

{
  "mcpServers": {
    "outlook-com": {
      "command": "C:\\Apps\\OutlookComMcp\\OutlookComMcp.exe",
      "args": []
    }
  }
}

Safety boundaries

No send tool exists.
No delete, move, archive, or send tool exists.
create_reply_draft is annotated as a non-read-only, non-idempotent tool so clients can require confirmation.
set_email_read_state is non-read-only but idempotent. It requires an exact email/store ID and never runs implicitly.
Reply-all defaults to false.
Search results, body size, scan count, calendar range, and reply body size are bounded.
stdout is reserved for MCP transport; application errors use stderr.
COM references are released after each operation.

Saving a draft is still a write operation. Review the recipients and content in Outlook before manually sending it.

Known limitations

Classic Outlook only; new Outlook does not expose the COM object model.
Folder listing and recursive search start from the default Inbox, Sent, Drafts, or a supplied folder ID. Whole-store and shared-store discovery are not yet implemented.
Recursive mail search is bounded to 100 folders, 10 levels, and 5,000 scanned items.
Calendar access currently uses the default calendar.
Body output is plain text. Rich HTML composition and signature insertion are not yet implemented.
Runtime integration tests require a Windows machine with a configured Outlook profile; CI runs unit tests without Outlook.

Development

The solution uses:

.NET 8
Official MCP C# SDK
xUnit.net v3
Windows GitHub Actions for build and unit tests

No Microsoft Graph dependency or Outlook credential is stored by this project.

License

This project is licensed under the MIT License. See LICENSE for details.