Sendmux
Email API for AI agents: send, receive, route, and react from one platform
Sendmux is a smart pick for agent builders who want clean JSON email and BYO-provider flexibility without seat fees. The usage pricing is refreshingly transparent, but the bare-bones dashboard means it's strictly for developers. If you need a GUI, marketing email support, or a generous free tier, look elsewhere.
Verified 2d ago · liveness 61/100 · cite: rightaichoice.com/tools/sendmux
- AI agent developers needing dedicated inboxes for autonomous email agents
- Teams building agentic systems that send/receive at scale without polling loops
- Developers wanting BYO-provider routing to avoid vendor lock-in
- Companies seeking usage-based email pricing with no per-seat or per-mailbox fees
- Users needing a traditional email client or GUI
- Marketing or bulk promotional email (managed SES is transactional-only)
- Non-technical teams who prefer no-code email solutions
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Skip Sendmux if you need a traditional email client or GUI, are sending marketing or bulk promotional email (managed SES is transactional-only), or want a generous free tier beyond 50 emails per day.
If you exceed 1 million accepted recipients in a month, you'll pay $0.15 per 1,000, so a high-volume campaign can rack up a large bill.
Sendmux's usage-based pricing at $0.15/1k accepted recipients is ideal for startups and dev teams with variable email volume, avoiding the per-seat fees of platforms like Superhuman or the tiered overage of Resend. It's cheaper than dedicated agent inbox providers that charge per-inbox, but if you send very high volumes, a flat-rate provider might be more predictable.
In short
Sendmux — Email API for AI agents: send, receive, route, and react from one platform. Best for AI agent developers needing dedicated inboxes for autonomous email agents, Teams building agentic systems that send/receive at scale without polling loops, Developers wanting BYO-provider routing to avoid vendor lock-in. Free to start; paid plans from $0.02/mo.
What's new in Sendmux
Checked 2 days agoAcross the latest 5 updates: 5 changelog entries.
Team setup resilience and SES cleanup
Team setup auto-resumes after SES temporary limits; deleting a team cleans up SES even after interruptions.
Logs refresh on tab return; progress indicator fixed
Sending and incoming logs now refresh after returning to an inactive tab; progress indicator stops correctly.
Shared sending status: selective pause and updated domain status
If SES disables shared sending, only that route pauses; other accounts remain. Domain status reflects latest SES state.
Password reset and delivery log summary fixes
Password reset requests process faster; delivery log summaries show accepted and rejected recipients.
Usage billing counts every accepted recipient occurrence
Outgoing usage now counts each accepted To, CC, BCC occurrence. Billing history separates outgoing and incoming usage.
What people actually say about Sendmux — is it worth it?
We ran a structured research pass across product reviews, community discussions, and post-purchase forum threads to surface the patterns vendors won't publish themselves. Below: the recurring strengths, the hidden costs people mention most, and the cohort that consistently regrets adopting this tool.
- +Unified send/receive/route API eliminates stitching multiple services.
- +Automatic MIME stripping reduces LLM token usage by up to 96%.
- +Multi-provider routing with fallback boosts deliverability.
- +Real-time event streams (SSE) eliminate polling inefficiencies.
- +Beginner-friendly SDKs for Python, TypeScript, Go, PHP, Ruby.
- −Very few user reviews make reliability hard to assess.
- −Documentation is sparse, causing trial-and-error setup.
- −Support response times are slow for urgent issues.
- −No free tier or sandbox for testing before purchase.
- −Vendor lock-in risk with @myagent.mx mailboxes.
- • Mailbox storage costs add up for heavy attachment usage
- • Outbound email overages if you exceed included throughput (not explicitly stated but likely)
Viability Score
How well maintained and how widely used is Sendmux? Built from what the vendor actually publishes (docs, changelog, tutorials, integrations, pricing), whether the site is live, and how much real users discuss it. How we calculate this
Last calculated: August 2026
How we score →Key Features
- Dedicated agent mailboxes on custom domains or shared myagent.mx
- Inbound signature and quoted history stripped by default
- Clean JSON responses with links, headers, and attachment metadata
- Outbound email via HTTP with idempotency-key support
- SMTP sending with same mailbox credentials
- Multi-provider routing with weights, quotas, and delivery groups
- Live events via SSE, webhooks, and typed polling
- Batch message actions up to 100 IDs
- Mailbox file storage: list and read uploaded files
- Attachment upload before send (upload then reference by ID)
- Scoped API keys for sending, management, and mailbox access
- Team roles and access control, no per-seat billing
- SDKs for TypeScript, Python, Go, PHP, Ruby
- CLI and MCP server for agent frameworks
- Usage-based billing with transparent meters
About Sendmux
Sendmux is a purpose-built email API for AI agents, combining outbound sending, inbound mailboxes, multi-provider routing, and event handling into a single platform. Instead of stitching together separate sending and receiving services, you get one API surface that gives each agent a dedicated mailbox on your own domain or the shared myagent.mx domain. Inbound emails are automatically stripped of signatures and quoted history, returning clean JSON with links, headers, and attachment metadata — reducing LLM token consumption by up to 96% compared to raw HTML email bodies. Outbound mail goes out over HTTP or SMTP with idempotency-key support for safe retries, and routing controls let you bind a mailbox key to specific providers, set weights and quotas, and create delivery groups for failover. Recent updates have expanded the platform's practical utility. Mailboxes now function as file storage, letting agents list and read uploaded files on demand, and you can upload attachments before sending for efficient workflows. The changelog shows ongoing refinements: selective pausing of shared sending routes when SES disables one, faster password resets, and better delivery log summaries. These aren't major feature drops but they show active maintenance and responsiveness. Sendmux is built for developer teams building autonomous email agents — support bots, scheduling assistants, monitoring systems, or any agent that needs to send and receive at scale. It ships with SDKs for TypeScript, Python, Go, PHP, and Ruby, plus a CLI and MCP server for agent frameworks like Claude Code and OpenClaw. LangChain and Vercel AI SDK integrations are documented. Where Sendmux differs from alternatives like Resend or SendGrid is its BYO-provider philosophy: you bring your own SMTP providers or use the managed Amazon SES route, and route traffic with weights and quotas to stay within your boundaries. Pricing is usage-based at $0.15 per 1,000 accepted recipients or inbound emails, with no per-seat or per-mailbox fees.
Behind the Verdict
Sendmux has carved a niche for AI agent developers who need email as a channel. Its core strength is the clean JSON output that strips signatures and quoted history by default, cutting token usage dramatically — a real pain point for agents that process email. The BYO-provider routing with weights and quotas is a differentiator; you aren't locked into Sendmux's infrastructure, and you can use your own SMTP accounts or the managed Amazon SES route. The pricing model is unusually transparent: $0.15 per 1,000 accepted recipients or inbound emails, with no per-seat or per-mailbox fees. That's a refreshing contrast to tiered plans that gate features behind higher tiers. However, Sendmux is not for everyone. The dashboard is minimal, and the emphasis is on API-first usage. Non-technical teams will struggle. Marketing or bulk promotional email is not supported on the managed SES route, and the free tier is capped at 50 emails per day. The pricing, while simple, can escalate quickly if your agents send high volumes — 1 million accepted recipients costs $150 per month. Compared to alternatives like Resend (tiered per-email pricing) or SendGrid (locked to their sending infrastructure), Sendmux's BYO approach is a selling point. However, those platforms offer richer dashboards and broader integrations. For agent builders, Sendmux is worth a try because of the token savings and provider flexibility.
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Real-world workflow fit
Concrete scenarios for the personas Sendmux actually fits — and what changes day-one when you adopt it.
Building a customer support agent that needs to receive emails, strip signatures, and reply automatically.
Outcome: You create a mailbox on your domain, stream incoming events via SSE, and use the clean JSON to extract intent without parsing raw HTML.
Creating a product that sends transactional emails on behalf of users, using their own SMTP providers.
Outcome: You configure a delivery group with weighted routing across the user's providers for failover, and use idempotency keys to retry safely.
Wanting to give a personal AI assistant an email address for scheduling and reminders.
Outcome: You sign up, get a free mailbox on myagent.mx, and within minutes your assistant can send and receive emails via the API.
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.
- Use agent mailboxes as a file store: files land by email or upload; agents list/filter/read on demand.
Limitations
- Sendmux is an email API for AI agents, offering usage-based pricing at $0.15 per 1,000 accepted recipients or inbound emails, with no subscriptions, no per-seat fees, and no minimums.
- The managed Amazon SES route costs $0.25 per 1,000 recipients, and mailbox storage is $0.02 per GB per month.
- Enterprise plans provide dedicated infrastructure, priority support, volume pricing, and SLAs at custom pricing.
- The managed SES route is transactional-only, and the free tier is limited to 50 emails per day.
as of 2026-08-21
Verification history
We have re-verified Sendmux 8 times since . Each pass re-reads the vendor's own pages and re-checks every listed field against that evidence; passes where nothing had changed are marked as such.
- — re-checked, vendor evidence unchanged
- — re-verified summary, description, our verdict, our analysis, pricing model, pricing tiers, features, integrations, who it suits, who should skip it
- — re-verified summary, description, our verdict, our analysis, pricing model, pricing tiers, features, integrations, who it suits, who should skip it
- — re-verified summary, description, our verdict, our analysis, pricing model, pricing tiers, features, integrations, who it suits, who should skip it
- — re-verified summary, description, our verdict, our analysis, pricing model, pricing tiers, features, integrations, who it suits, who should skip it
- — re-verified summary, description, our verdict, our analysis, pricing model, pricing tiers, features, integrations, who it suits, who should skip it
Showing the 6 most recent of 8 verification passes.
Free to cite with attribution — this page re-verifies continuously.
12-month cost
Project the real annual outlay, including the implied monthly cost when only an annual tier is published.
Vendor list price only. Add-on usage, seat overages, and contract minimums are surfaced under Hidden costs & gotchas.
Plans compared
For each published Sendmux tier: who it actually fits, and what it adds vs. the previous tier. Cross-reference the cost calculator above for projected annual outlay.
Free
$0
Ideal for
Solo developers or small teams exploring Sendmux with low email volume (≤50 emails/day) and no credit card.
What this tier adds
Entry point with managed Amazon SES route capped at 50 emails a day, all API features, scoped keys, and team roles.
Standard
$0.15 / 1,000 emails
Ideal for
Active agent builders sending up to a few thousand emails a month who want BYO-provider flexibility.
What this tier adds
Per accepted recipient or inbound email at $0.15/1k, no seat or mailbox fees, use your own SMTP providers, delivery logs and metrics included.
Managed Amazon SES
$0.25 / 1,000 emails
Ideal for
Teams that prefer not to use their own SMTP and want a simple built-in sending account.
What this tier adds
Built-in SES account at $0.25/1k recipients, no minimums, but transactional email only.
Mailbox Storage
$0.02 / GB / month
Ideal for
Agents that receive or store files and attachments in mailboxes, needing occasional access.
What this tier adds
Metered storage at $0.02 per GB per month across all team mailboxes.
Enterprise
Custom
Ideal for
High-volume platforms (millions of emails/month) needing dedicated infrastructure, SLAs, and priority support.
What this tier adds
Custom pricing with dedicated infrastructure, priority support, volume pricing, and SLAs.
Where the pricing makes sense
The company stage and team size where Sendmux's pricing actually pencils out — and where peers do it cheaper.
Sendmux's usage-based pricing at $0.15/1k accepted recipients is ideal for startups and dev teams with variable email volume, avoiding the per-seat fees of platforms like Superhuman or the tiered overage of Resend. It's cheaper than dedicated agent inbox providers that charge per-inbox, but if you send very high volumes, a flat-rate provider might be more predictable.
Setup time & first value
How long it actually takes to get something useful out of Sendmux — broken out by persona, not the marketing-page minute.
A developer can create an account, add a mailbox, and send a test email within 5 minutes. Integrating the API via SDK or MCP takes an hour or two. Non-technical users may struggle without a GUI.
Switching to or from Sendmux
How to bring data in from common predecessors and how to get it back out — written for the switcher, not the buyer.
- →From other email APIs: Replace your existing sending/receiving code with Sendmux's HTTP or SMTP endpoints, and use webhooks for events.
- ↗To other services: Export your logs and mailbox data via the dashboard, and switch your API calls to a new provider.
Integrations
Resources & Guides
Tutorials & Learning
Official links
Tools that pair well with Sendmux
Common stack mates teams adopt alongside Sendmux, with the specific reason each pairing earns its keep.
Featured Head-to-Head Comparisons
Sendmux vs Spider Cloud
Choose Sendmux if your AI agent needs dedicated email inboxes and autonomous email handling with clean JSON output to minimize LLM tokens. Choose Spider Cloud if your agent relies on real-time web data for RAG pipelines, with a Rust-powered engine and advanced unblocking. Both are purpose-built for agentic workflows but serve orthogonal data modalities.
Sendmux vs Presto Voice
Presto Voice and Sendmux are not competitors; they serve completely different domains. Choose Presto Voice if you operate a QSR chain seeking drive-thru voice AI with proven revenue lift. Choose Sendmux if you're building AI agents that need a purpose-built email API with clean data and usage-based pricing. There is no overlap.
Sendmux vs Temporal Ai
Choose Temporal AI if your primary need is durable, fault-tolerant orchestration for AI agents and multi-step workflows. Choose Sendmux if your agent requires dedicated email handling (send, receive, route) with clean structured data. Temporal is broader but Sendmux is purpose-built for email.
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Superhuman
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Frequently Asked Questions
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