Buy a forwarding inbox (username@stableemail.dev) for $1 USDC / 30 days via MPP micropayment.
What it does
This endpoint purchases a forwarding inbox on stableemail.dev. For $1 USDC, you get `username@stableemail.dev` active for 30 days. The inbox can forward inbound email to a real address, act as a programmatic mailbox (with messages readable via API), or both. No API keys or accounts are needed — authentication and payment happen via the x402/MPP protocol using USDC on Base, Solana, or Tempo. Usernames must be 3–30 characters, lowercase alphanumeric plus hyphens. If `forwardTo` is omitted, message retention is enabled automatically so messages can be fetched programmatically via the `/api/inbox/messages` endpoints.
The inbox is part of the broader StableEmail platform, which also offers pay-per-send email ($0.02/email from a shared relay address), custom subdomains ($5 one-time), subdomain sending ($0.005/email), and inbox management endpoints (top-up, cancel with pro-rata refund, update forwarding, read/delete messages). Bulk top-up discounts are available: 90 days for $2.50 (17% savings) and 365 days for $8 (34% savings). Anyone can top up any inbox without wallet ownership verification.
The endpoint is a POST that returns HTTP 402 with an MPP/x402 payment challenge. After signing and attaching the USDC payment, the response includes the inbox address, expiration date, and days remaining. Cancellation at any time yields a pro-rata on-chain USDC refund. Message content and attachments are retained for 90 days. The recommended agent integration path is via `agentcash-skills` (`npx -y agentcash@latest`), which handles payment negotiation automatically.
Capabilities
Use cases
- —AI agents that need a dedicated receiving email address for sign-ups or notifications
- —Creating disposable forwarding addresses for privacy without account registration
- —Programmatic email reception — read inbound messages via API for automation workflows
- —Agents or bots that need to both send and receive email under a consistent address
- —Temporary project-specific email addresses with automatic expiration
Fit
Best for
- —AI agents needing email receive capability without traditional email provider accounts
- —Developers wanting accountless, API-key-free email inboxes paid via crypto micropayments
- —Privacy-conscious users who want forwarding aliases purchasable with a wallet
- —Automated workflows that need to programmatically read inbound emails
Not for
- —High-volume transactional email sending (this is an inbox purchase endpoint, not bulk send)
- —Users without crypto wallets or USDC — payment requires x402/MPP-compatible client
- —Long-term permanent email addresses (requires periodic top-ups to stay active)
Quick start
# Buy an inbox via agentcash CLI
npx agentcash fetch POST https://stableemail.dev/api/inbox/buy \
--body '{"username": "alice", "forwardTo": "alice@gmail.com"}'Example
Request
{
"username": "alice",
"forwardTo": "alice@gmail.com"
}Response
{
"inbox": "alice@stableemail.dev",
"success": true,
"expiresAt": "2025-08-16T00:00:00.000Z",
"daysRemaining": 30,
"retainMessages": true
}Endpoint
Quality
Full OpenAPI 3.1 schema with detailed request/response documentation, clear pricing ($1 USDC), and comprehensive guidance text. The probe returned 405 (not 402) because HEAD/GET were used on a POST-only endpoint, but the endpoint is confirmed live via the OpenAPI spec and the root page (200). Slight deduction for no captured 402 challenge on this specific endpoint and no dedicated docs page (404).
Warnings
- —Probe returned 405 because HEAD/GET were tried on a POST-only endpoint; the endpoint itself is live per OpenAPI and landing page
- —No dedicated /docs page exists (returns 404); all documentation is in the OpenAPI x-guidance field and landing page
- —forwardTo is optional — omitting it creates a programmatic-only mailbox; agents should be aware of this default behavior
Citations
- —Inbox costs $1 USDC for 30 dayshttps://stableemail.dev
- —Payment via x402/MPP using USDC on Base, Solana, or Tempohttps://stableemail.dev
- —Username rules: 3-30 chars, lowercase alphanumeric + hyphenshttps://stableemail.dev/.well-known/x402
- —forwardTo is optional — omit it to use as a programmatic mailbox with retainMessages enabled automaticallyhttps://stableemail.dev/.well-known/x402
- —Cancel anytime for a pro-rata refundhttps://stableemail.dev
- —Bulk discounts: 90 days for $2.50 (save 17%), 365 days for $8 (save 34%)https://stableemail.dev
- —Message content and attachments retained for 90 dayshttps://stableemail.dev/.well-known/x402
- —Recommended agent integration via agentcash-skills (npx -y agentcash@latest)https://stableemail.dev/.well-known/x402