Email Inbox API + Sending by Sendmux

Name: Email Inbox API + Sending by Sendmux
Author: Sendmux

by Sendmuxversion 2.2.0i★ –iComputer or cloud

Registry nameio.github.Sendmux/sendmux-mcp

Install

Overview

Description from the maker (original English)

AI email inbox and sending tools with attachments, search, live events, and webhooks.

PopNx MCP’s three pillars

These three are never merged into one score: opinions, measurements and popularity are different things.

User voiceiNo reviews yetReviews open together with accounts in a later step
Our basic checksi1 of 1 passedChecked from public information; code not scanned yet
UsageiNot measured yet★ –

What you can do with it

We have not written a plain-language summary for this one yet. Below are the facts we read from the registry.

Connection: Computer or cloud
Transport: stdio, Streamable HTTP
Category: Chat & email

Install

Pick the AI app you use, then copy the settings.

Before you install

Basic checks: 1 of 1 passed
Runs on the maker’s server: what you ask it goes through their server.
The registry lists no key to fill in.

You need

Runs in the cloudNothing to install; it connects over the internet
npmNode.js installed (for the npx command)

Which app do you use?

ClaudeClaude CodeCursorVS CodeChatGPT

Pick your app above. We remember it, so next time the button says “Install in …”.

Works in Claude on the web, desktop and mobile:

Open Settings → Connectors
Press Add custom connector
Paste the address below and press Add
If it asks you to sign in, sign in with the maker

https://mcp.sendmux.ai/mcp

Or run it on your computer

Open Claude Desktop → Settings → Developer → Edit Config, and paste this into claude_desktop_config.json

{
  "mcpServers": {
    "sendmux": {
      "command": "npx",
      "args": [
        "-y",
        "sendmux-mcp"
      ]
    }
  }
}

Run this in your terminal

claude mcp add --transport http sendmux https://mcp.sendmux.ai/mcp

Or run it on your computer

claude mcp add sendmux -- npx -y sendmux-mcp

Open in Cursor

Or copy the settings yourself

Paste into .cursor/mcp.json in your project, or ~/.cursor/mcp.json

{
  "mcpServers": {
    "sendmux": {
      "url": "https://mcp.sendmux.ai/mcp"
    }
  }
}

Or run it on your computer

Open in Cursor

Or copy the settings yourself

Paste into .cursor/mcp.json in your project, or ~/.cursor/mcp.json

{
  "mcpServers": {
    "sendmux": {
      "command": "npx",
      "args": [
        "-y",
        "sendmux-mcp"
      ]
    }
  }
}

Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.

Open in VS Code

Or copy the settings yourself

Paste into .vscode/mcp.json in your project

{
  "servers": {
    "sendmux": {
      "type": "http",
      "url": "https://mcp.sendmux.ai/mcp"
    }
  }
}

Or run it on your computer

Open in VS Code

Or copy the settings yourself

Paste into .vscode/mcp.json in your project

{
  "servers": {
    "sendmux": {
      "type": "stdio",
      "command": "npx",
      "args": [
        "-y",
        "sendmux-mcp"
      ]
    }
  }
}

Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.

ChatGPT connects only to servers on the internet:

Open ChatGPT on the web → Settings → Connectors (Apps)
Press Create or Add (some plans need Developer mode under Advanced first)
Paste the address below, give it a name and save
If it asks you to sign in, sign in with the maker

https://mcp.sendmux.ai/mcp

Menu names can differ slightly by plan and over time.

Your choice stays on this device in a cookie; no account needed.

These settings are generated from the maker’s registry entry. If the README says otherwise, follow the README.

What it can do

We have not read this server’s tool list yet; we check endpoints in rotation.

Basic checksi

We check information anyone can see; we have not read the code. Checks that do not apply are left out of the count. · Checked Nov 7, 2026

✓ Pass
Maker matches the repo
The registry name was verified with the GitHub account Sendmux, which owns the repo
… Not checked yet
Still maintained
We have not read this repo from GitHub yet
… Not checked yet
Has a licence
We have not read this repo from GitHub yet
… Not checked yet
Endpoint responds
Not checked yet; we check endpoints in rotation
… Not checked yet
Sign-in with OAuth
Not checked yet; we check endpoints in rotation
… Not checked yet
No hidden instructions in tool descriptions
Not checked yet; we read the tool list when we check the endpoint

Compared with others in Chat & emaili

More stars than 0% of the other 1777 servers in this category
Published to the registry more recently than 43% of the other 1777 servers in this category
Basic checks equal to or better than 100% of the other 1777 servers in this category

Compared with every active server in this category in the registry. Stars count only when the publisher owns the repo.

Common questions

Is Email Inbox API + Sending by Sendmux safe?

It passed 1 of 1 applicable basic checks. We have not read the code. Before adding a key or token, see what access the server asks for and use a key with only the permissions you need.

What keys or codes does it need?

The registry does not list a required key, though some servers ask you to sign in on first use.

Does it run on my computer or in the cloud?

Either way works: install it on your computer or connect to the cloud version.

Is it still maintained?

The GitHub repo last changed –, and the latest version (2.2.0) reached the registry 36 days ago.

Which apps can use it?

Apps that support MCP, such as Claude Desktop, Claude Code, Cursor and VS Code. It connects by URL, so apps that accept remote MCP servers work too, such as ChatGPT in developer mode.

What can I use instead?

In the same category: Vexa, emailmd, MCP WhatsApp Cloud

Alternatives

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Reading a card:★ GitHub starsiThree pillars: reviews · checks · usageiUpdated = latest version published to the registryi

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by Vexa-ai

Meeting bot and transcripts for Google Meet, Teams and Zoom. Live or after, speakers labelled.

Runs in the cloud★ 2,949Apache-2.0Updated 2 months ago

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emailmd

by anypost

Render markdown into email-safe HTML, lint drafts for deliverability problems, and preview emails.

Computer or cloud★ 1,385MITUpdated 31 days ago

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MCP WhatsApp Cloud

by codespar

MCP server for WhatsApp Cloud API (Meta) — messages, media, and templates via Graph API

Runs on your computer★ 277MITUpdated 5 months ago

Install

README from the maker

Open the README

Copied from the maker’s repo as written. PopNx MCP has not reviewed or endorsed it. HTML, images and scripts are removed. Links lead off this site.

Email Inbox API + Sending by Sendmux

Email inbox API, inbound mail, and outbound sending MCP and A2A servers for AI agents, with inbound email, clean JSON parsing, webhooks, and multi-provider routing through Sendmux.

This package is the Sendmux MCP. Keep it separate from any documentation-search MCP used by docs tooling.

Documentation

Sendmux docs: sendmux.ai/docs
Management API reference: sendmux.ai/docs/api/introduction
Mailbox API reference: sendmux.ai/docs/mailbox-api/introduction
Sending API reference: sendmux.ai/docs/sending-api/introduction
Source repository: qubrics/qubrics-sdk

Requirements

Python 3.10 or newer.
A send-capable smx_mbx_* key or owner-approved Sending-resource smx_agent_* token for Sending tools.
A mailbox-scoped smx_mbx_* key or scoped smx_agent_* token for Mailbox tools.
A root smx_root_* key for Management tools.

2.0.0 upgrade

Version 2.0.0 removes local file_path and roots inputs from MCP attachment tools. Before upgrading a self-managed package or server, retain the prior known-working package environment, dependency state, and MCP client and tool configuration. Update attachment callers to use the attachment workflow for agents, then verify tool discovery and each attachment workflow your agents use.

To roll back a self-managed installation, restore the retained package environment, dependency state, and MCP client and tool configuration together. Verify tool discovery and the relevant attachment workflow before resuming agents. A package rollback doesn't reverse uploads or sends that have already completed.

For clients that use Sendmux's hosted endpoint, changing a local pip environment doesn't change the deployed server version. A hosted deployment rollback is a separate operator release action and must be verified against the hosted endpoint.

Installation

pip install sendmux-mcp

Usage

Run a single local server with the per-surface commands.

QUBRICS_API_KEY=smx_mbx_... sendmux-mcp-mailbox

QUBRICS_API_KEY=smx_root_... sendmux-mcp-management QUBRICS_API_KEY=smx_mbx_... sendmux-mcp-sending

Run a combined local server with sendmux-mcp.

QUBRICS_MCP_SURFACES=mailbox,sending \

QUBRICS_MAILBOX_API_KEY=smx_mbx_... \ QUBRICS_SENDING_API_KEY=smx_mbx_... \ sendmux-mcp

Run all three local surfaces when you have both key types.

QUBRICS_MCP_SURFACES=mailbox,management,sending \

QUBRICS_MAILBOX_API_KEY=smx_mbx_... \ QUBRICS_MANAGEMENT_API_KEY=smx_root_... \ QUBRICS_SENDING_API_KEY=smx_mbx_... \ sendmux-mcp

The generic sendmux-mcp command also accepts --surface or --surfaces. The wrapper commands select exactly one surface.

Transports

stdio is the default transport for local agent clients.

QUBRICS_API_KEY=smx_mbx_... sendmux-mcp-mailbox --transport stdio

http and streamable-http expose the MCP endpoint over HTTP. HTTP mode defaults to 127.0.0.1:8765/mcp and requires a separate MCP bearer token unless you explicitly opt out.

QUBRICS_API_KEY=smx_mbx_... \

QUBRICS_MCP_HTTP_BEARER_TOKEN=local-mcp-token \ sendmux-mcp-mailbox --transport http --host 127.0.0.1 --port 8765 --path /mcp

/health returns a small JSON health response for the selected surfaces.

Hosted Endpoint

The public hosted MCP endpoint is https://mcp.sendmux.ai/mcp.

For hosted clients, use HTTP transport with OAuth. Do not add manual Authorization headers, API keys, custom OAuth endpoints, or custom scopes unless your client explicitly requires them.

Hosted OAuth clients that omit requested scopes during registration or authorization are supported; the server advertises the hosted scope set through discovery and bearer challenges.

The packaged sendmux-mcp-hosted command runs the hosted server runtime. Local and private deployments should use the local commands above unless you are operating a compatible OAuth-backed hosted environment.

Hosted A2A Endpoint

The same hosted runtime exposes deterministic A2A 1.0 over HTTP+JSON at https://a2a.sendmux.ai/a2a/v1. Discover it from https://a2a.sendmux.ai/.well-known/agent-card.json; OAuth resource metadata is at https://a2a.sendmux.ai/.well-known/oauth-protected-resource.

Send exactly one JSON DataPart to the A2A message:send operation. Its data selects a curated Sendmux operation and supplies that operation's inputs:

"operationId": "managementListDomains", "pathParameters": {}, "query": { "limit": 10 }, "headers": {}, "body": null, "mailboxId": null }

operationId uses the same curated operation IDs as the hosted MCP service. OAuth grants are audience-bound to the A2A resource and retain their Sendmux surface and permission limits. The service returns one JSON DataPart containing the upstream status, safe response headers, and JSON body (or bodyBase64 for non-JSON responses).

The A2A endpoint is immediate and stateless: streaming, push notifications, persistent tasks, and task cancellation are not advertised or routed.

Configuration

Setting	Environment	Default
Tool surfaces	`QUBRICS_MCP_SURFACES`	required for `sendmux-mcp`; wrapper commands select one surface
API key fallback	`QUBRICS_API_KEY`	accepted for compatible single-key setups
Mailbox API key	`QUBRICS_MAILBOX_API_KEY`	required when mailbox is selected unless a compatible fallback is provided
Management API key	`QUBRICS_MANAGEMENT_API_KEY`	required when management is selected unless a compatible fallback is provided
Sending API key	`QUBRICS_SENDING_API_KEY`	required when sending is selected unless the fallback key is a send-capable `smx_mbx_` key or owner-approved Sending-resource `smx_agent_` token
App API base URL	`QUBRICS_APP_BASE_URL`	`https://app.sendmux.ai/api/v1`
Sending API base URL	`QUBRICS_SENDING_BASE_URL`	`https://smtp.sendmux.ai/api/v1`
Transport	`QUBRICS_MCP_TRANSPORT`	`stdio`
HTTP host	`QUBRICS_MCP_HOST`	`127.0.0.1`
HTTP port	`QUBRICS_MCP_PORT`	`8765`
HTTP path	`QUBRICS_MCP_PATH`	`/mcp`
HTTP bearer token	`QUBRICS_MCP_HTTP_BEARER_TOKEN`	required for HTTP unless opt-out is enabled
Allow unauthenticated HTTP	`QUBRICS_MCP_ALLOW_UNAUTHENTICATED_HTTP`	`false`
Allowed browser origins	`QUBRICS_MCP_ALLOWED_ORIGINS`	no browser origins
Snapshot directory override	`QUBRICS_MCP_OPENAPI_INPUT_DIR` or `OPENAPI_INPUT_DIR`	packaged snapshots
App snapshot override	`QUBRICS_MCP_APP_OPENAPI`	packaged app snapshot
Sending snapshot override	`QUBRICS_MCP_SENDING_OPENAPI`	packaged sending snapshot
Request timeout	`QUBRICS_MCP_TIMEOUT_SECONDS`	`30`
Retry attempts	`QUBRICS_MCP_RETRY_MAX_ATTEMPTS`	`3`
Retry time budget, in seconds	`QUBRICS_MCP_RETRY_MAX_ELAPSED_SECONDS`	unset

Retries honour Retry-After and X-RateLimit-Reset without applying the local backoff ceiling, and stop for retryable: false. Set the optional retry budget with RetryConfig(max_elapsed_seconds=30), the environment variable above, or --retry-max-elapsed-seconds 30. A retry that would exceed the remaining budget returns the original error; in-flight requests keep their normal HTTP timeouts.

Packaged OpenAPI snapshots are the default so released tool names, schemas, and descriptions stay stable. Path, directory, and URL overrides are available for development, canary, and debugging runs.

Tool Surfaces

Mailbox: tools for granted mailboxes, profile/session discovery, messages, attachments, bounded message waits, threads, folders, search, counts, and mailbox sends. Requires an smx_mbx_* key or scoped smx_agent_* token. Agent tokens remain limited by server-side scopes; pre-claim self-registered agent tokens do not include email.send.
Management: tools for domains, mailboxes, logs, metrics, spend summary, and webhooks. Requires an smx_root_* key.
Sending: tools for attachment upload refs, single sends, and batch sends. Requires an smx_mbx_* key or owner-approved Sending-resource smx_agent_* token.

The server rejects keys with the wrong prefix before starting.

Package Contract For Maintainers

The source checkout includes sendmux_mcp/mcp-contract.json, generated from the actual server factory's public tool discovery. Use its tools.by_surface entries and tools.count instead of maintaining a separate catalogue. Each entry retains the tool's description, input/output schemas, and annotations. The contract also separates hosted resource, local transports, API origins, certified protocol revisions, and the runtime versions used during generation.

After installing a build that contains the contract, read it without credentials or network requests:

from sendmux_mcp.contract import load_contract

contract = load_contract() print(contract["package"])

The result identifies the installed distribution and version. load_contract() raises ValueError for stale source/version evidence, a mismatched pinned FastMCP runtime, or unsupported certified revisions. The recorded transitive MCP version is provenance, not a narrower dependency constraint. Reading the artifact does not certify a newly resolved dependency version or prove a deployed service matches this build.

uploads distinguishes the locally enforced inline and Mailbox byte caps from Sending's returned max_size_bytes authority. The Sending presign request schema does not impose a numeric maximum; use the upload intent response, not a historical source constant. URL expiry and physical attachment retention are not equivalent, and this artifact does not certify storage cleanup.

From the repository root, pnpm generate:mcp refreshes native editable metadata and writes deterministic contract bytes. With that environment prepared, pnpm exec .tmp/python-venv/bin/python -m sendmux_mcp.contract --check checks freshness without rewriting. pnpm build:mcp verifies tests, wheel/sdist inclusion, installed consumption, and frozen conformance checks. Checkout changes are not available through pip install until their release is published.

Attachment Workflow For Agents

Use qubrics_mailbox_wait_for_message when a user asks an agent to wait for new mail. The tool is bounded; if it returns matched=false, call it again rather than holding an MCP tool call open indefinitely.

When a message has attachments:

Call qubrics_mailbox_read_attachment with message_id and attachment_id when you need the attachment contents.
For small text-like attachments, read the returned text.
For binary or oversized attachments, use the returned resource_link / download_url promptly outside model context.
Use qubrics_mailbox_get_attachment only when metadata is enough or you need to refresh the link.

Use qubrics_mailbox_upload_attachment for outbound attachments over MCP. It accepts exactly one input mode:

presign_upload_url=true for hosted MCP or shell-capable agents; upload the file to the returned URL with exact headers and no API key, then send with the returned blob_id.
content_base64 only for tiny agent-authored files, capped at 32 KiB decoded. If it is

Only the beginning is shown; read the rest in the repo

Email Inbox API + Sending by Sendmux

Overview

PopNx MCP’s three pillars

What you can do with it

Install

Before you install

Or run it on your computer

Or run it on your computer

Or run it on your computer

Or run it on your computer

What it can do

Basic checksi

Maker matches the repo

Still maintained

Has a licence

Endpoint responds

Sign-in with OAuth

No hidden instructions in tool descriptions

Compared with others in Chat & emaili

Common questions

Alternatives

Vexa

emailmd

MCP WhatsApp Cloud

README from the maker

Email Inbox API + Sending by Sendmux

Documentation

Requirements

2.0.0 upgrade

Installation

Usage

Transports

Hosted Endpoint

Hosted A2A Endpoint

Configuration

Tool Surfaces

Package Contract For Maintainers

Attachment Workflow For Agents