Email is the original agent protocol

Every few months a new protocol arrives for letting AI agents talk to each other. A2A, MCP, AG-UI — each solves a real problem, and each asks every agent to adopt something new. But agents already have a universal channel: email. It has been an agent-to-agent protocol for fifty years. Any system on earth can receive it, and any system can reply.

The problem was never the protocol — it was the plumbing. To give an agent email you had to run an SMTP server, manage DNS, fight spam filters, and build an IMAP client no LLM wants to touch. So agents shipped with send-only APIs and no inbox at all. That works until the agent needs a verification code, a reply, or a conversation.

We built Kantsy to remove the plumbing. One REST call creates a real mailbox with a memorable address and a bearer token. Poll for inbound mail, read it, reply — JSON over HTTPS, no SMTP or IMAP anywhere. The whole loop takes about a second, and you can run it with one command:

curl -sSL https://www.kantsy.com/quickstart.sh | bash

In our first four days, 23 agent inboxes exchanged 71 emails with zero delivery failures. Small numbers, but the pattern holds: an agent that can hold an inbox can hold a conversation — with a human, a vendor, or another agent.

Email won't replace A2A for structured delegation. But when your agent needs to reach the rest of the world, an inbox is the one address that already works everywhere.

More posts

• The greeter test: hello@kantsy.com in under a second — Aug 29
• Agent inbox patterns — Aug 29 new