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Roshan Jonnalagadda
Roshan Jonnalagadda

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Sendmux CLI: email inbox API in your terminal

#cli #email #agents #api

Install Sendmux CLI

A lot of agent email testing starts with the same awkward loop: send a message, refresh a dashboard, copy JSON, then guess what your agent will see.

Sendmux CLI cuts that loop down to the terminal.

It gives developers and AI agents direct access to Sendmux: an email inbox API for AI agents and SaaS platforms. You can create and manage mailboxes, search inbound mail, send email, inspect API responses, and script the same workflows your app or agent will run later.

If your AI agent needs to receive email, triage messages, search an inbox, reply to a thread, or send outbound mail through a controlled email sending API, the CLI is the fastest way to prove the flow.

What Sendmux does

Sendmux gives software and AI agents a proper email layer.

Instead of stitching together a sending provider, IMAP access, inbound parsing, webhooks, API keys, mailbox storage, and agent tooling by hand, Sendmux puts those surfaces behind one API platform.

The complete email API platform includes the following:

  • Email Inbox API for receiving, searching, reading, and managing agent inboxes
  • Sending API for outbound email from a mailbox
  • Management API for teams, domains, mailboxes, API keys, routing, and platform controls
  • SDKs for TypeScript, Python, Go, PHP, and Ruby
  • MCP for authorised AI agent access
  • CLI for terminal workflows, scripts, debugging, and automation

That means Sendmux can act as an email inbox API, inbound email API, email sending API, SMTP API, and agent mailbox layer from one system.

Why the CLI exists

Email infrastructure gets painful when the first question is, "Where do I test this?"

With Sendmux CLI, the terminal becomes the control surface.

You can list mailboxes, inspect messages, search snippets, send test emails, and verify API behaviour in the same environment where your agent, scripts, or CI jobs already run.

Here's why that matters:

  • You can test an agent inbox before wiring it into an app
  • You can search inbound email without building a UI
  • You can send a controlled outbound email from a mailbox
  • You can debug API responses with machine-readable JSON
  • You can manage Sendmux resources in scripts
  • You can validate scoped API keys before handing them to an agent
  • You can prototype email workflows before moving them into an SDK

Install 

brew install sendmux/tap/sendmux
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or:

npm install -g @sendmux/cli
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Then configure local profiles so you do not pass keys on every command:

sendmux profiles:set management --api-key smx_root_...
sendmux profiles:set mailbox --api-key smx_mbx_...
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Management commands use smx_root_ keys. Mailbox and sending commands use smx_mbx_ keys.

The CLI checks key prefixes before making the API call, so the wrong key type fails early instead of hitting the network.

Three workflows that show the shape of it

listing Sendmux mailboxes from the terminal

1. List agent mailboxes

A platform or agent operator can list the mailboxes available in a Sendmux workspace.

This helps before assigning inboxes to agents, checking mailbox provisioning, or confirming a management key can see the expected resources.

searching an inbox with the email inbox API

2. Search inbound email

Agents need more than raw email delivery. They need searchable, structured access to messages.

With the Email Inbox API through the CLI, you can search snippets in an agent inbox and return clean JSON for another process to read.

The result:

  • Find the latest invoice email
  • Search unread support messages
  • Pull matching messages into a triage script
  • Check whether an external service sent a verification email

sending email from a Sendmux mailbox

3. Send outbound mail

Sendmux also handles outbound email.

From the CLI, you can send through the Sending API using a mailbox-scoped key. You can include idempotency keys for safer retries and use JSON output when another tool needs to process the result.

This fits agent replies, transactional email tests, workflow notifications, and scripted operational mail.

Built for humans and agents

The CLI is designed for developers at a terminal and agents that need predictable output.

By default, API commands print readable JSON. Add --json when you need machine-readable output for scripts, agent tools, or automation.

The CLI also supports practical API flags:

  • --body for inline JSON request bodies
  • --body-file for request payloads from disk
  • --query for query parameters
  • --path for path parameters
  • --header for extra headers
  • --idempotency-key for safer send retries
  • --if-match and --if-none-match where supported by the API operation

The command set is generated from Sendmux public API surfaces. The current CLI includes 95 generated API operation commands: 40 Mailbox commands, 52 Management commands, and 3 Sending commands.

Where CLI fits beside MCP and SDKs

Sendmux gives you a few ways to work, depending on where the task lives.

Use MCP when an AI agent should call authorised Sendmux tools directly. Sendmux has Documentation MCP for searching docs and Product MCP for authorised Management, Mailbox, and Sending tools.

Use SDKs when you are building application code. Sendmux SDKs are available for TypeScript, Python, Go, PHP, and Ruby.

Use CLI when you want terminal control: one-off checks, local testing, scripts, CI jobs, debugging, and agent-friendly JSON workflows.

A simple way to choose:

  • MCP is for agent tool access
  • SDKs are for application code
  • CLI is for terminal workflows
  • APIs are the underlying contract

Why this matters for AI agents

AI agents increasingly need to deal with real-world systems that still use email.

Verification emails. Invoices. Support threads. Customer replies. Vendor notices. Billing alerts. Operational messages.

A normal inbox is built for a human with a mouse. An AI agent needs an API.

Sendmux gives agents a programmable inbox, outbound email, webhooks, Server-Sent Events for mailbox updates, scoped API keys, MCP tools, and SDKs. The CLI gives developers the quickest way to inspect and prove those workflows before shipping them.

Try it

Install the CLI, create a mailbox-scoped key, and run a small workflow:

  1. List a mailbox
  2. Search for a message
  3. Send a test email
  4. Repeat the same flow from an SDK or MCP-enabled agent

That is the point of Sendmux CLI: email infrastructure you can see, test, script, and hand to agents without leaving the terminal.

Top comments (4)

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alaadeen profile image
Alaadin •

nice

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m_muajhid profile image
M Muajhid •

yutu

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asmyshlyaev177 profile image
Alex •

Interesting, but Gmail from script can do the trick as well.

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roshan_jonnalagadda_ced3c profile image
Roshan Jonnalagadda •

Gmail doesn't provide agent-specific mailboxes, but we do :) so this would be ideal for that. We also let you monitor what your agents are up to with a unified inbox – something Gmail won't do either. And lastly, you can bring in any provider you like – set quotes (e.g., send 3 emails from this Gmail account, 2 from this Hotmail, etc.), and our system does just that – routes your emails with ease.