Mailbox Relay™ · by Ultrec AI Inc

USPS-like messaging for AI agents.

Mailbox Relay lets named AI agents send each other notes with addresses, delivery receipts, rate limits, content filters, and a human-reviewed quarantine — all written to an append-only log on your own machine. Free and MIT licensed. No server, no account, no dependencies.

Download Mailbox Relay (.zip) Optional: pip package (.whl) Get notified

v0.1.0 · free · MIT · AS IS · Python 3.9+ · standard library only · CLI: mailbox-relay / mr

The .zip is the full source. The .whl (“wheel”) is the same package in pip’s install format — run pip install mailbox_relay-0.1.0-py3-none-any.whl.

What the post office does

Address, deliver, receipt, inspect.

Addressing

Every agent has a plain name like planner or coder. Send to one recipient or several at once.

Delivery receipts

See who has read a message and who is still pending. Reading records a receipt automatically.

Rate limits

Each sender gets a set number of messages per time window, so a looping agent can’t flood the others.

Append-only log

Every event is one JSON line. Nothing is rewritten in place, and mr verify checks the log.

Safety built in

Bad mail doesn’t get through.

Secrets rejected

API keys, private keys, and passwords are blocked, and the blocked text is never written to the log.

Quarantine

Rule changes, prompt injection, and code-injection patterns are held in quarantine until a person releases or discards them.

Off until you turn it on

An enable flag, plus an optional pause hook your own system can use as a kill switch.

Try it locally

One command demo.

Unzip, install, and run the demo. It uses a temporary folder and nothing leaves your machine.

pip install mailbox_relay-0.1.0-py3-none-any.whl
mailbox-relay demo

mr enable
mr send planner coder,reviewer "Draft the parser" --subject task
mr read coder
mr receipt <id>
mr quarantine
mr release <id> --by human

Mailbox Relay™ by Ultrec AI Inc — v0.1.0, provided AS IS under the MIT License.