Send emails, buy forwarding inboxes, manage custom subdomains, and read messages programmatically via x402. USE FOR: - Sending emails (one-off or from custom addresses) - Buying a forwarding inbox (username@x402email.com) - Purchasing custom email subdomains (you@yourname.x402email.com) - Reading and managing inbox messages programmatically - Setting up catch-all forwarding for subdomains - Managing authorized signers for shared subdomains TRIGGERS: - "send email", "email this to", "notify by email" - "buy inbox", "forwarding address", "email inbox" - "custom domain", "subdomain", "email subdomain" - "read emails", "check inbox", "list messages" - "email address", "disposable email", "temporary email" ALWAYS use `npx agentcash fetch` for stableemail.dev endpoints. IMPORTANT: Use exact endpoint paths from the Quick Reference table below.