Mailtrap × Claude Agent SDK

Email-driven coding agent: an engineer mails a bug or feature request to a Mailtrap Inbound address. The Claude Agent SDK implements the change on a target repository, opens a GitHub pull request, and replies in the same Mailtrap thread with the PR link. Follow-up mail in that thread (Mailtrap Threads) continues the loop.

What this exercises

• Inbound — custom domain webhook at POST /webhook
• Threads — follow-ups are keyed by Mailtrap thread_id and resume the Claude session
• Replies — in-thread response via the inbound reply API (not a new conversation)
• Email API — the reply is sent outbound; every agent message uses category coding-agent (X-MT-Category)

Prerequisites

1. Mailtrap account with a verified sending domain and inbound custom domain (MX on that domain). See Inbound and receiving emails.
2. Inbound webhook pointing at this server: https://<your-host>/webhook (webhooks).
3. Anthropic API key
4. GitHub Personal Access Token with repo scope (create at GitHub → Settings → Developer settings → Personal access tokens). A GitHub App installation token works the same way if you set it as GITHUB_TOKEN.
5. gh is not required on PATH; the Agent SDK uses git/gh via its Bash tool if gh is installed. Install GitHub CLI so the agent can open PRs.

Setup

cp .env.example .env
# fill in the values below
npm install
npm start

Point the Mailtrap inbound webhook at POST /webhook on this host.

Environment

Variable	Description
ANTHROPIC_API_KEY	Claude API key
MAILTRAP_API_TOKEN	Mailtrap API token
MAILTRAP_INBOX_ID	Inbound inbox ID (used if the webhook payload omits it)
DEFAULT_FROM_EMAIL	Address on the inbound custom domain (required for replies)
GITHUB_TOKEN	PAT or GitHub App token
TARGET_REPO	owner/name of the repository to fix
PORT	HTTP port (default 3000)

Flow

1. Mail dev@your-domain with a bug report.
2. Webhook loads the message and thread, runs the Agent SDK (Read / Edit / Bash / tests) on TARGET_REPO.
3. Agent opens a GitHub PR and this server replies in-thread with the PR URL (category coding-agent).
4. Reply in the same thread (e.g. “please also update the tests”). The agent resumes that thread’s session, pushes another commit, and replies again.

References

• Mailtrap API
• Mailtrap Inbound
• Inbound messages / replies
• Inbound threads
• Email categories (X-MT-Category)
• Claude Agent SDK

License

MIT — see LICENSE.txt.