Sendmux
An email API platform for AI Agents integrates sending, inbox, calendar and file storage into a single interface. The official stated that received emails can be output as structured JSON with signatures and quotes removed, which greatly reduces parsing costs, and it supports multi-service provider routing and automatic failover.
Updated: 2026-10-27
What is Sendmux?
Sendmux's official positioning is "an email API for AI Agents". It integrates the previously separate sending services and inbox services into a single platform: an AI Agent can send and receive emails, manage calendars and store files through a single API. It provides access methods including HTTP API, SMTP, SDK, CLI and hosted MCP, and the official claims that it takes no more than five minutes to start sending emails from scratch.
Who is it for?
- Developers and automation engineers who need to equip AI Agents with real email sending and receiving capabilities.
- Teams that build customer service or operational AI Agents using frameworks such as Claude, LangChain, and AI SDK.
- Platforms that provide Agent hosting services to customers and require multi-tenant isolation.
- Independent developers who are tired of piecing together email sending services and inbox services.
Key features
6Agent-specific Inbox
You can create a dedicated email address for each Agent on a verified domain or the shared myagent.mx. Emails are returned as clean, structured JSON, with signatures and quote history removed by default. Links, headers, and attachment metadata are retrieved on demand.
Token-Efficient Content Interface
In the official example, the same raw email contains 3247 tokens, but only 127 tokens after being structured by Sendmux. Agents do not need to waste computing power parsing HTML layouts.
Multi-service Email Sending Routing
It can connect to Gmail, SendGrid, Mailgun, Resend, or any SMTP-compatible service providers. The official claims that it supports weighted distribution and automatic failover, and traffic will be automatically rerouted when a service provider fails.
Unified Inbox Dashboard
All Agent mailboxes are viewed in one place, supporting full-database search, keyboard shortcut operations, batch processing of up to 50 threads, and color label management.
Event Streaming & Quotas
The official claims that emails are received in real-time via Server-Sent Events (SSE) without polling. Sending quotas are controlled at the second, minute, hourly, and daily levels, and the platform is said to support sending over 10 million emails per day.
Multi-tenancy & API Keys
One account can create multiple isolated workspaces. API keys can be restricted to only read and write a specific mailbox, making it suitable for customer-facing Agent platforms.
How to use Sendmux
- 1First, use the 2 free mailboxes provided by the official, complete OAuth authorization access via the managed MCP endpoint, and get the sending and receiving functions working before writing business logic.
- 2When an Agent reads emails, always request structured JSON content and enable signature removal and quote stripping to control context costs.
- 3Add an idempotency key to outgoing emails to prevent duplicate messages caused by Agent retries; test with the built-in account first before switching to your own service provider.
- 4Create separate mailboxes for different Agents and use mailbox-specific API keys for easy auditing and recycling.
- 5Check the quota and compliance requirements in the official documentation before launch to avoid triggering service provider risk controls.
Traffic & popularity
Data month Sep 2026
Sendmux receives about 607 visits per month and ranks #29,874,365 worldwide.
Monthly visits
7 monthsTraffic sources
- Direct30.1%
- Search28.1%
- Referrals12.9%
- Display ads8.3%
- Social6.9%
- Other13.8%
Top countries
- United States100.0%
Estimated from third-party traffic data.
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