How to Send Email with Bitcoin Lightning
Instantly. Anonymously. No account, no SMTP, no setup.
The Problem with Sending Email Today
Sending a single email programmatically requires a surprising amount of infrastructure. A provider account with verified domain and DNS records. DKIM, SPF, and DMARC configured. API keys rotated and stored. Monthly fees even for low-volume use. Terms of service that can suspend your account without warning.
For a human who wants to send one-off messages without tying their identity to the content, or for an autonomous agent that needs to fire a notification email without a provisioned SMTP account, the entire setup is wildly out of proportion to the task.
What Sats4AI Offers
Sats4AI's email service sends email to any address for a flat rate of 200 sats. No SMTP account. No domain verification. No signup. Provide the recipient, subject, and body — the Lightning payment proves authorization — and the email is delivered.
Available from the browser for human use, and via L402 API, MCP server, or OpenClaw for automated and agent-driven workflows.
For Humans
The web interface is the fastest way to send a one-off email without setting anything up. Go to sats4ai.com/email, fill in the recipient, subject, and body, pay the 200-sat Lightning invoice, and the email is sent.
When Would You Actually Use This?
Contact without revealing your address
The email sends from a relay address, not yours. Set a reply-to if you want responses. If you don't, your email never appears.
Testing a contact form or integration
Need to verify an email arrives correctly without configuring an entire sender domain? Send one, see what it looks like, move on.
Sending from a machine with no email setup
You're SSH'd into a server, writing a quick script, or using a device with no email client or credentials configured.
No account, no commitment
Don't want another provider account for occasional use. Pay 200 sats, send the email, done.
For Agents
This is where the real value lies. An autonomous agent that needs to send an email today has to either be pre-configured with SMTP credentials at build time, or it has to ask for them at runtime. Both require out-of-band setup before the agent can act.
With the L402 email API, the agent sends an HTTP request, receives a Lightning invoice in the 402 response, pays it using its Lightning wallet, and resends with the payment proof. No credentials to store. No accounts to provision. The payment is the authorization.
Agent Use Cases
Server and infrastructure alerts
DevOpsMonitoring script detects a disk filling up or a service going down. It calls the email API, pays 200 sats, and your on-call engineer receives the alert in seconds. No environment variables to configure.
Transactional notifications from prototypes
PrototypingBuilding fast and need to send an order confirmation or status update? Instead of integrating a full email provider, your backend makes one HTTP call. It works today, and you can swap it out when the product scales.
Autonomous agent pipelines
AI AgentsAn AI agent using the MCP server can research a topic with AI chat, compose a summary, and email it to a recipient — all without any human-configured email credentials in the pipeline.
Multi-step notification chains
AutomationAn agent detects an event, sends an SMS for immediate attention, and follows up with a detailed email containing a full report. Both paid in sats, both via API, no accounts needed for either.
Scheduled digests
ScheduledA cron job scrapes data, summarizes it with an AI model, and emails the digest to recipients. Each send is a separate 200-sat payment — costs scale perfectly with actual use.
L402 API — Three-Step Flow
Send the request without auth
The server returns 402 Payment Required with a Lightning invoice in the www-authenticate header.
Pay the invoice
Any Lightning wallet returns a preimage after payment.
Resend with the preimage
Include Authorization: L402 <macaroon>:<preimage>. The server verifies the payment and sends the email.
Or use lnget to handle the entire flow in one command:
lnget POST https://sats4ai.com/api/l402/email \
--json '{"to":"recipient@example.com","subject":"Hello","body":"Message body here"}'Full API docs with curl and Python examples at sats4ai.com/l402/email.
MCP Server
AI agents connected to the Sats4AI MCP server call the email tool directly. The agent handles payment automatically — no credential passing needed.
OpenClaw
Agents using the OpenClaw protocol discover the service in the registry, negotiate payment, and send email — fully autonomous.
What You Should Know
| Parameter | Details |
|---|---|
| Price | 200 sats flat per email |
| Coverage | Any valid email address worldwide |
| Format | Plain text only — no HTML |
| Subject limit | 200 characters |
| Body limit | 10,000 characters |
| Sender | Relay address — use replyTo to receive replies |
| Footer | "Routed via Sats4AI.com" footer appended automatically |
| Token | Single-use — each invoice covers exactly one email |
| API access | L402, MCP, OpenClaw |
Why Pay for Email with Bitcoin?
The question answers itself when you consider what the payment replaces: account verification, domain authorization, API keys, terms of service, and monthly fees. A Lightning payment is cryptographic proof of authorization — no identity, no account, no contract required.
Built-in spam prevention
At 200 sats per email, bulk abuse is economically unattractive. The payment is the spam filter.
Borderless by design
No geographic restrictions or payment processor approvals. If you have sats, you can send email.
No vendor lock-in
The API is stateless. Each request stands alone. Your pipeline isn't tied to any provider's account status.
Scales with actual use
Send one email a year or ten thousand. You pay for exactly what you send. No minimums, no tiers, no overages.
Try It Now — No Signup Required
200 sats. No account. No SMTP setup. Send your first email in under 60 seconds.