Sendmux
PaidEmail API for AI agents: send, receive, route, and react with one platform.
By Tanmay Verma, Founder · Last verified 03 Jul 2026
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Added 7d ago
77/100Safe BetIn short
Sendmux — Email API for AI agents: send, receive, route, and react with one platform. Best for AI agent developers needing dedicated email inboxes for autonomous agents, Teams building agentic systems that send/receive emails at scale, Developers seeking a unified API for sending, receiving, and routing email. Plans from $0.02/mo.
Is Sendmux actually worth it?
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Editorial Verdict
Best for
AI agent developers needing dedicated email inboxes for autonomous agentsTeams building agentic systems that send/receive emails at scaleDevelopers seeking a unified API for sending, receiving, and routing emailUsers who want to bring their own email providers (e.g., custom SMTP) to avoid vendor lock-inCompanies wanting usage-based pricing with no per-seat or per-mailbox fees
Not ideal for
Users needing a traditional email client or GUI interface (web interface is limited to settings/dashboard)Marketing or bulk promotional email (Sendmux restricts managed SES to transactional; own providers can be used but platform is agent-focused)Non-technical users who prefer no-code email solutionsTeams that require free tier beyond 50 emails/day managed SES cap
Sendmux delivers a purpose-built email API for AI agents that slashes token waste with intelligent JSON parsing. The usage-based pricing and bring-your-own-provider model offer flexibility, but the lack of a visual email client may limit adoption outside developer teams.
Compare with: Sendmux vs Poke (Interaction Co.)
Last verified: July 2026
What's new in Sendmux
Checked 7 days agoAcross the latest 4 updates: 2 feature updates and 2 changelog entries.
FeatureChangelog·7 days agoNewest
Mailbox upload URLs, CLI local files, SDK file helpers
Mailbox API now supports presigned upload URLs for attachments. CLI and SDKs can attach local files without base64 encoding.
ChangelogChangelog·8 days ago
Bug fix: transactional email contrast and readability
Fixed light backgrounds and text contrast in transactional emails for better readability across inboxes.
FeatureChangelog·8 days ago
Transactional email UI fixes and Mailbox API download URLs
Transactional emails now have better contrast. Mailbox attachment metadata includes short-lived download URLs.
ChangelogChangelog·9 days ago
SMTP envelope validation fix
SMTP now validates envelope addresses before delivery path selection, preventing MAIL FROM required rejections.
Viability Score
77/100
Safe BetHow likely is Sendmux to still be operational in 12 months? Based on 4 signals — momentum (how recently it shipped), wrapper dependency, revenue model, and web presence.
momentum
55
funding runway
80
website health
90
wrapper dependency
100
Last calculated: July 2026
How we score →Key Features
- Dedicated agent mailboxes on custom domains or shared myagent.mx
- Outbound email via HTTP or SMTP with idempotency-key support
- Inbound email with signature and quoted history stripping by default
- Structured JSON responses (text, links, headers, attachment metadata) reducing LLM token usage
- Multi-provider routing with weights, quotas (second/minute/hour/day), and delivery groups
- Live events via SSE streams, webhooks (delivery, receipt, spam), and typed polling
- Batch message actions (up to 100 IDs per request)
- Management API for teams, keys, billing, and logs
- Mailbox API to read messages and threads
- Attachments up to 10 per send request
- Scoped API keys for sending, management, and mailbox access
- Team roles and access control (no per-seat billing)
- Dashboard with delivery logs, usage metrics, and deliverability monitoring
- SDKs in TypeScript, Python, Go, PHP, Ruby
- CLI and MCP server for AI agent integration
About Sendmux
PaidIntermediateAPI availableAPI · CLI · Web
Sendmux is an email infrastructure API designed specifically for AI agents. It provides dedicated mailboxes, multi-provider sending, and live inbox events so that agents can handle email independently. The platform strips signatures and quoted history by default, delivering clean JSON that reduces token consumption. It supports sending via HTTP or SMTP, with idempotency keys for safe retries, and offers routing controls such as provider weights, quotas, and delivery groups. Developers can subscribe to webhooks, SSE streams, or typed polling for real-time event handling. Unlike traditional email APIs, Sendmux is built from the ground up for agentic workflows, eliminating the need to stitch together separate sending and receiving services. Pricing is usage-based at $0.15 per 1,000 standard emails (send or receive via your own providers) or $0.25 per 1,000 via the managed Amazon SES route, with mailbox storage at $0.02/GB/month. There are no per-seat, per-mailbox, or tiered fees, making it cost-effective for high-volume agent deployments. The platform also offers SDKs for Python, TypeScript, Go, PHP, and Ruby, a CLI, an MCP server, and pre-built skills for AI agent frameworks.
Behind the Verdict
Sendmux fills a clear gap: existing email APIs aren't designed for autonomous agents. By stripping signatures and quoted history, it reduces a typical email from 3,247 tokens to 127—a 96% saving that directly cuts LLM costs. The multi-provider routing with weights and quotas is a standout feature for production deployments. That said, the platform is API-only—there's no web-based email client for manual oversight. For agent-heavy workflows, that's fine; for hybrid teams wanting human-in-the-loop, you'll need to pair it with a separate interface. Compared to general-purpose transactional email APIs like SendGrid or SES, Sendmux offers unified send/receive and agent-friendly JSON, but at a higher per-email cost if you're not optimizing for token savings. The free tier caps managed SES at 50 emails/day, so serious testing requires a payment method. Overall, it's a smart pick for AI-first teams that need clean inbox data at scale.
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Use Cases
- Give your AI agent a dedicated email address to receive and respond to customer inquiries autonomously.
- Route incoming support emails to the appropriate agent based on content and sender rules, stripping signatures to save tokens.
- Send transactional receipts or notifications from your agent via HTTP/SMTP with idempotency for safe retries.
- Monitor email deliverability and provider health across multiple sending accounts from a single dashboard.
- Stream live email events (received, sent, spam) to your agent for real-time decision-making.
Limitations
- Sendmux is primarily API-driven; there is no full-featured email client GUI.
- Managed Amazon SES is capped at 50 emails/day on sign-up (can be raised) and is restricted to transactional email only.
- The platform does not support marketing or bulk promotional sends through its managed route.
- All features are accessible on the pay-as-you-go plan, but deep customization (e.g., dedicated infrastructure) requires enterprise pricing.
12-month cost
Project the real annual outlay, including the implied monthly cost when only an annual tier is published.
Annual total
$2
Over 12 months
Effective monthly
$0
Billed monthly
Vendor list price only. Add-on usage, seat overages, and contract minimums are surfaced under Hidden costs & gotchas.
Integrations
Amazon SESSMTP
Resources & Guides
Frequently Asked Questions
Tools that pair well with Sendmux
Common stack mates teams adopt alongside Sendmux, with the specific reason each pairing earns its keep.
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