langchain-sendmux

LangChain toolkit for Sendmux, the email API for AI agents.

Gives an agent its own mailbox: it can send email, read what arrives, and reply from its own address.

Requirements

• Python 3.10 or newer
• langchain-core v1

Installation

pip install langchain-sendmux

Getting an API key

For API-key authentication, use a key that can both send and receive. Two ways to get one:

• Dashboard — create a mailbox and a mailbox-scoped key (smx_mbx_*). See API keys.
• Agent self-registration — the agent claims its own @myagent.mx mailbox and gets an smx_agent_* token, with no human signup first. See email for AI agents.

Note on agent tokens: a freshly self-registered smx_agent_* token can read and receive, but cannot send until a human owner has been invited and has approved it. Until then send_email and reply will fail. A dashboard smx_mbx_* key with send permission works immediately.

Read the key from the environment. Never hard-code it.

OAuth access tokens

Set access_token to a bare REST OAuth token or callable instead of api_key:

import os
from langchain_sendmux import SendmuxToolkit

toolkit = SendmuxToolkit(
    access_token=lambda: os.environ["SENDMUX_ACCESS_TOKEN"],
    default_from="agent@yourdomain.dev",
)
tools = toolkit.get_tools()

The provider runs before every tool request. Your application owns protected token storage, expiry checks, and refresh coordination. Request mailbox.read and email.send to use all three tools, and select one mailbox at consent; these tools do not supply a mailbox selector. Credentials are excluded from the toolkit's representation and model serialisation. See REST OAuth.

Quick start

import os

from langchain.agents import create_agent

from langchain_sendmux import SendmuxToolkit

smx = SendmuxToolkit(
    api_key=os.environ["SENDMUX_API_KEY"],
    default_from="agent@yourdomain.dev",
)

agent = create_agent(
    model="gpt-4o",
    tools=smx.get_tools(),
    system_prompt="You triage the support inbox.",
)

agent.invoke(
    {"messages": [{"role": "user", "content": "Reply to anyone asking about pricing."}]}
)

Tools

SendmuxToolkit(...).get_tools() returns three tools.

send_email

Sends through your configured sending providers, to any recipient.

var_from is spelt that way because from is a reserved word in Python.

list_messages

Lists messages in the agent's own mailbox, newest first.

reply

Sends from the agent's own mailbox address, rather than through a sending provider. Use this to answer someone who wrote in.

Configuration

SendmuxToolkit(api_key=..., default_from=...)

Retries and duplicate sends

Agents retry. Pass idempotency_key on send_email and reply and Sendmux will send once, even if the same call arrives several times inside 24 hours. Any stable string works — a task id, a thread id, a hash of the message.

Details: idempotency.

Common errors

Related

• Quickstart
• Mailboxes
• All Sendmux SDKs
• Pricing — usage-based, no per-seat or per-mailbox fees

Licence

MIT. See the licence file.