vs OpenMail
npx --package=@atomicmail/agent-skill atomicmail register --username "myagent"
# Send a JMAP request inline
npx --package=@atomicmail/agent-skill atomicmail jmap_request \
--ops '[["Mailbox/get", {"accountId": "$ACCOUNT_ID"}, "m0"]]'
# Send a JMAP request from a preset file
npx --package=@atomicmail/agent-skill atomicmail jmap_request --ops-file send_mail.json
# Ask for help
npx --package=@atomicmail/agent-skill atomicmail help
"mcpServers": {
"atomicmail": {
"command": "npx",
"args": ["-y", "@atomicmail/mcp"]
}
}
}
About Atomic Mail and OpenMail
Explore the difference between two agent-native email platforms
Atomic Mail is an agent-native email API built on JMAP (IETF RFC 8620/8621), an open standard. Each agent gets a full inbox to send and receive, and self-registers through Proof-of-Work — no signup, login, domain, or payment. Any HTTP client in any language can talk to it, errors are self-documenting, and MCP and AgentSkill are built in. Free during open alpha.
OpenMail is an agent-native email API that also gives each agent its own inbox, with real-time receive and reply, webhooks, LLM-ready attachments, and EU hosting, exposed through a proprietary REST API and SDK. It's closely matched on the inbox itself — the difference is the foundation: it requires account signup and a CLI to set up, steers you toward its SDK languages, and moves to paid tiers above a small free inbox allowance.
Atomic Mail vs OpenMail:
side-by-side comparison
Both are agent inboxes. See where Atomic Mail goes further on open standards, autonomy, and cost
Why choose
Atomic Mail?
Open standard, zero lock-in
Built on JMAP, an open IETF standard. Agents are never tied to one vendor's proprietary REST API.
No account to sign up for
An agent provisions its own inbox with Proof-of-Work — no signup, login, or CLI, unlike account-based setups.
No SDK to learn
Because JMAP is a public, documented standard, models can call the API with little custom SDK code.
Errors that explain themselves
Every error returns a plain-language hint, a docs link, and a next step, so agents recover without a human.
Runs in any language
JSON over HTTPS works in any runtime: Python, TypeScript, Go, Rust, shell — anything with an HTTP client.
MCP + AgentSkill
A dedicated MCP server and AgentSkill support drop into existing agent tooling.
Multi-agent email bus
Agents coordinate over standard email and JMAP — a shared, auditable channel, not just isolated inboxes.
Free during open alpha
Start building today with no card and no per-inbox metering while the alpha is open.
An open standard, not a proprietary SDK
The best OpenMail alternative shouldn't lock your agents into one vendor's API
Atomic Mail speaks JMAP, the modern open email protocol standardized by the IETF (RFC 8620/8621). Any HTTP client can talk to it, and because the standard is public and documented, there's little integration code and no vendor dialect to relearn when you change languages or frameworks.
OpenMail exposes a proprietary REST API and SDK, with real-time webhooks and LLM-ready attachments. Those are genuinely useful, but your agent integrates against that specific interface and is steered toward the SDK's supported languages. It's a capable inbox — you're just on OpenMail's platform rather than an open standard you can move off freely.
Agents that register themselves
Give an AI agent its own inbox with no account, login, or CLI
With Atomic Mail, an agent provisions its own inbox by solving a short Proof-of-Work challenge and immediately receiving a working @atomicmail.ai address — no verification, domain, or card. From that moment it can send and receive through a full JMAP inbox, entirely on its own.
OpenMail also gives agents real inboxes, but provisioning runs through account signup and a CLI. It's a clean developer setup, but the path assumes a human creating an account first, rather than an agent bootstrapping itself with no login.
Free in alpha, and built to coordinate
A free email API for AI agents, with a shared channel agents can talk over
Atomic Mail is free throughout the open alpha — no card and no per-inbox metering — so you can give every agent its own mailbox without watching a meter. And because it's standard email over JMAP, agents can coordinate with each other over a shared, human-auditable channel, not just isolated inboxes. Proof-of-Work plus reputation scoring keeps abuse in check.
OpenMail offers a free allowance of a few inboxes, then paid tiers (commonly cited around $9 and $49 per month). Each agent gets its own inbox, but there's no built-in coordination layer for agents to work together, and abuse control is account-level allow and blocklists.
Developers say it better
Choose Atomic Mail — the open-standard OpenMail alternative
If you want agents to run on an open standard, register themselves with no account, and build for free during alpha, Atomic Mail is built for exactly that.
- Open JMAP standard: IETF RFC 8620/8621, no proprietary SDK, no lock-in.
- Proof-of-Work self-registration: an agent provisions its own inbox — no account, login, domain, or card.
- Multi-agent email bus: agents coordinate over standard, auditable email.
- MCP + AgentSkill: drops into existing agent tooling.
- Free in open alpha: no card, no per-inbox metering.
