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Sendmux

The Email API for AI Agents·sendmux.ai

Sendmux is an email API for AI agents and SaaS platforms that combines multi-provider outbound sending, agent inboxes, dedicated inbound mailboxes, team-scoped controls, webhooks, Server-Sent Events, and usage-based billing. Teams can send through their own connected providers (SMTP, Gmail, Microsoft 365, Amazon SES) or a managed Amazon SES route, then read replies through the Mailbox API, IMAP, webhooks, or live events. It returns inbound mail as clean, structured JSON instead of raw HTML, with signatures and quoted history stripped by default.

What it's for

AI customer support agent inboxesAI sales outreach agent email sending and reply trackingAI scheduling agent email negotiation and booking confirmationAI monitoring agent alert email ingestion and escalationmulti-tenant email infrastructure for SaaS platforms

Features 19

@sendmux/cli command-line tool
Agent inboxes on @myagent.mx or custom domains
Attachment handling up to 25MB (inline for ≤10MB, presigned URL for ≤25MB)
Automatic thread grouping by Message-ID and References headers
Batch message actions up to 100 IDs
Clean JSON email content with signatures and quoted history stripped by default
Custom domain provisioning with atomic DNS verification, re-checked every 6 hours
Delivery groups with provider weights and quotas (second/minute/hour/day)
Delivery logs and usage metrics on every account
Idempotency-Key support for safe retries
MCP servers for documentation search and authorised Sendmux tools
Multi-provider outbound email routing with weighted distribution and automatic failover
One credential across REST, SSE, IMAP, and SMTP
SDKs for TypeScript, Python, Go, PHP, and Ruby
Sender rules with allowlist/denylist modes; rejected mail not billed
Server-Sent Events live mailbox event stream
Signed HMAC-SHA256 webhooks for delivery and mailbox events
Team-based multi-tenancy with mailbox-scoped API keys
Unified inbox dashboard across all agent mailboxes

At a glance

free tierAPI

TypeWeb app

DeploymentCloud

PlatformsWeb

ForAI agent builders, multi-tenant SaaS platforms, software teams and agents, enterprises running fleets of AI agents

CompanySendmux

Integrations

GmailSendGridMailgunResendAmazon SESMicrosoft 365LangChainClaude CodeOpenClaw

Resources

Pricing

Pricing is usage-based with no per-seat or per-mailbox fees: $0.15 per 1,000 standard emails (sent via own providers or received), $0.25 per 1,000 via the managed Amazon SES route, and $0.02 per GB/month for mailbox storage. Enterprise pricing is custom/quote-based for higher volumes.

Free to startFree

Free to start, no credit card required

Managed Amazon SES route capped at 50 emails a day by default (raisable in one click); pay only once email flows

Pay as you goQuote

No per-seat fees, no per-mailbox fees, no minimum commitments

EnterpriseQuote

Same API and usage model, no per-seat tax; priced around volume by custom agreement

For volumes past a few million emails a month