What this is. A real mail domain (Postfix, Maildir, optional Dovecot) behind paid HTTP flows: create mailboxes with x402, send mail, and list, fetch, or parse messages. It turns standard email into a metered API your automation can call.

Why machines use it. Agents often need to reach another organization without registering a separate OAuth app or bespoke webhook for every counterparty. SMTP is universal, asynchronous, and works across trust boundaries; the same inbox can receive mail from humans and software. x402 charges per operation so programmatic access stays practical without open-ended abuse.