Send mail any way you like
Submit by API as one message, a batch of up to a thousand, or raw email, or over standard SMTP, and schedule messages for later delivery.
‹ qOS
Agent Email· Sentio
Email that goes both ways.
Sentio is a complete email engine rewritten from scratch in Rust. It does not just send: it runs a full inbound mail server that receives, authenticates, virus-scans, and classifies every message that arrives. An agent can fire off a thousand messages and, on the same platform, have replies parsed, scored, and handed back as structured data, all behind a clean API and the full authentication stack mailbox providers now demand.
Two-way sends and receives real mail
30+ email RFCs implemented
3-tier spam and abuse defense
Why Sentio
Send-only was never the whole job.
Email tooling forces a bad trade. Legacy mail servers are powerful but have no API, no multi-tenancy, and bolt on authentication and spam filtering through external daemons. Cloud APIs are easy but send-only and closed, and you do not control your data.
Sentio does the full job, sending, receiving, authenticating, and filtering, with the developer experience of a modern API but on your own servers, with your own data.
Capabilities
What it can do.
Receive and understand inbound mail
A full standards-compliant inbound server accepts mail, parses every part, and routes each message by address, pattern, domain, or catch-all to a webhook.
Authenticate every message
Outbound mail is cryptographically signed; inbound mail is checked against SPF, DKIM, DMARC, and ARC, with the verdict stamped into a standard header.
Three-tier spam defense
A sub-millisecond connection guard with bans, rate limits, blocklists, and greylisting, then self-learning content scoring, then an optional AI tiebreaker only for borderline messages.
AI classification of incoming mail
A language model categorizes uncertain messages as legitimate, commercial, unsolicited, or harmful and adjusts the verdict, invoked only on the small borderline slice to keep cost down.
Virus scanning before storage
Every inbound attachment is scanned and infected mail rejected before anything is written to disk.
Engagement tracking
Optional open and click tracking with bot-open detection, device and client parsing, and geolocation, over your own branded tracking domains.
Sending reputation stays isolated
Per-customer rate limits, independently-learning spam filters, dedicated or shared IP pools, and gradual IP-warming, so one sender can never drag down delivery for everyone else.
Built different
Why it is not just another mail API.
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Genuinely two-way
Most email APIs are send-only. Sentio runs a real inbound mail server that receives, authenticates, scans, classifies, and delivers structured data to a webhook. The inbound pipeline is fully built, not a stub.
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The full modern auth stack in one binary
DKIM, SPF, DMARC, ARC, MTA-STS, DANE, and BIMI discovery, all implemented natively, instead of stitching three external daemons around a 25-year-old mail server.
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Rust from the ground up
A thirteen-crate async engine with zero-copy parsing and memory safety by construction, not a patched legacy mail server.
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AI in the pipeline, not stapled on
Language-model classification is a native tier of the spam engine, gated to the borderline band so it touches only a small fraction of volume, with a choice of cloud or self-hosted models.
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Self-hosted with SaaS-grade developer experience
A REST API, signed webhooks, OAuth 2.0, OpenAPI docs, and full metrics and tracing, but you own the data and the servers.
By the numbers
Standards, end to end.
30+email RFCs
SPF/DKIM/DMARC/ARCinbound verification
1,000messages per batch call
700+tests across the engine
Agent-first
An agent's inbox and outbox at once.
An agent treats Sentio as its mailbox and its outbox together: it sends with one API call and receives replies as structured webhook events, so an email back-and-forth becomes a normal API loop instead of a scraping problem. Inbound mail arrives already parsed, authenticated, virus-scanned, and spam-scored, with an AI category attached, so the agent gets a clean decision surface, not a raw mailbox.
- Send a single message, a batch, or raw email, with scheduling and automatic signing.
- Receive and triage: every message routed to a webhook with authentication results and an AI category.
- Draft contextual replies per inbound route, with sending on the roadmap.
Put Agent Email to work.
See HQ running in your own Slack or Teams, on the operating system we built for agents.