How to use Claude to build a private agent email channel
The author and Claude Code built sixel.email for owner-only agent email and validated replies, then used inbox polling as a heartbeat to detect when the agent goes offline.
news.ycombinator.com
Prompt to try
Editorial adaptation, not the source author’s exact prompt. Replace bracketed inputs and review tool permissions first.
Help build [private agent email service] with one API key, a send endpoint restricted server-side to [owner address] and an inbox endpoint for replies. Validate replies with DKIM and drop unknown senders. Use inbox polling as a heartbeat and alert [owner] when [polling timeout] is exceeded.
Reach people exploring AI agents
See placements →What happened
The author reports a free, open-source owner-only email channel whose inbox polling also alerts them when the agent goes quiet.
Reported by sixel-et on Hacker NewsHow the agent did it
- Worked with Claude Code on background side projects and encountered pauses for questions.
- Built owner-only sending and DKIM-validated reply endpoints with the agent.
- Used inbox polling as a heartbeat to alert when the agent stops checking.
Where a person stepped in
The author answers agent questions by email; the post does not describe formal code review or security audit steps.
A person approved each step before the agent continued.
The author used Claude Code on side projects while working elsewhere. When the agent got stuck waiting for an answer, progress paused until they checked back. They wanted email questions and replies, but only through a private channel between themselves and the agent.
They and their agent built sixel.email with two endpoints and one API key. POST /v1/send lets the agent email only its owner, with the recipient restriction enforced by the server. GET /v1/inbox lets the agent retrieve replies. Incoming messages are DKIM-validated, and unknown senders are dropped. The author contrasts this design with giving an agent a full inbox open to outside senders.
They then realized inbox polling could also monitor whether the agent was still running. The poll acts as a heartbeat: if the agent stops checking for messages, sixel.email notices and alerts the owner. The author says a previous agent crash went unnoticed for six hours, whereas the new channel lets them know when it goes quiet without separate health-check infrastructure.
The source describes the project as free, open source and usable with anything that has curl. It does not describe a formal security audit or code review.
Who it's for: People running background agents who need a restricted question-and-reply channel and alerts when an agent stops polling.
Prompt
Suggested prompt (written by Agents In Use, not the author's)
Source: Hacker News · sixel-et
Frequently asked questions
Who can send messages through the channel?
The agent can email only its owner, enforced by the server. Replies are DKIM-validated, and messages from unknown senders are dropped.
How does the heartbeat work?
The agent polls the inbox for replies. The source says sixel.email notices when polling stops and alerts the owner, using the same channel as a liveness monitor.
More details
About this account
Claude Code worked on side projects while the author was occupied and helped build the private email channel.
Platform: Hacker News. Attribution: https://news.ycombinator.com/item?id=47234295. Prompt: Suggested (written by Agents In Use, not the author's). Sourced by the Agents In Use pipeline.
Credit: sixel-et on Hacker News
Source published 3 Mar 2026
Source checked 14 Oct 2026
Tools and topics
Claude Code · sixel.email · DKIM · curl
Agent communication · Email · Heartbeat monitoring
Editorial completeness: 100/100. Measures documented fields, not agent performance or verified outcomes.