agent-email-inbox

name agent-email-inbox description Use when building any system where email content triggers actions — AI agent inboxes, automated support handlers, email-to-task pipelines, or any workflow processing untrusted inbound email. Always use this skill when the user wants to receive emails and act on them programmatically, even if they don't mention "agent" — the skill contains critical security patterns (sender allowlists, content filtering, sandboxed processing) that prevent untrusted email from controlling your system. license MIT metadata {"author":"resend","version":"3.0.4","homepage":"https://resend.com/agent-skills","source":"https://github.com/resend/resend-skills","openclaw":{"primaryEnv":"RESEND_API_KEY","requires":{"env":"[Truncated]"},"envVars":["[Truncated]","[Truncated]","[Truncated]","[Truncated]","[Truncated]","[Truncated]"],"links":{"repository":"https://github.com/resend/resend-skills","documentation":"https://resend.com/docs/agent-email-inbox-skill"}}} inputs [{"name":"RESEND_API_KEY","description":"Resend API key for sending and receiving emails. Get yours at https://resend.com/api-keys","required":true},{"name":"RESEND_WEBHOOK_SECRET","description":"Webhook signing secret for verifying inbound email event payloads. Returned as `signing_secret` in the response when you create a webhook via the API.","required":false}] references ["security-levels.md","webhook-setup.md","advanced-patterns.md"] AI Agent Email Inbox Overview This skill covers setting up a secure email inbox that allows your application or AI agent to receive and respond to emails, with content safety measures in place. Core principle: An AI agent's inbox receives untrusted input. Security configuration is important to handle this safely. Why Webhook-Based Receiving? Resend uses webhooks for inbound email, meaning your agent is notified instantly when an email arrives. This is valuable for agents because: Real-time responsiveness — React to emails within seconds, not minutes No polling overhead — No cron jobs checking "any new mail?" repeatedly Event-driven architecture — Your agent only wakes up when there's actually something to process Lower API costs — No wasted calls checking empty inboxes Architecture Sender → Email → Resend (MX) → Webhook → Your Server → AI Agent ↓ Security Validation ↓ Process or Reject SDK Version Requirements This skill requires Resend SDK features for webhook verification ( webhooks.verify() ) and email receiving ( emails.receiving.get() ). Always install the latest SDK version. If the project already has a Resend SDK installed, check the version and upgrade if needed. Language Package Min Version Node.js resend >= 6.9.2 Python resend >= 2.21.0 Go resend-go/v3 >= 3.1.0 Ruby resend >= 1.0.0 PHP resend/resend-php >= 1.1.0 Rust resend-rs >= 0.20.0 Java resend-java >= 4.11.0 .NET Resend >= 0.2.1 Install the resend npm package: npm install resend (or the equivalent for your language). For full sending docs, install the resend skill. Quick Start Ask the user for their email address — You need a real email address to send test emails to. Ask the user and wait for their response before proceeding. Choose your security level — Decide how to validate incoming emails before any are processed Set up receiving domain — Configure MX records for the user's custom domain (see Domain Setup section) Create webhook endpoint — Handle email.received events with security built in from the start. The webhook endpoint MUST be a POST route. Set up tunneling (local dev) — Use Tailscale Funnel (recommended) or ngrok. See references/webhook-setup.md Create webhook via API — Use the Resend Webhook API to register your endpoint programmatically. See references/webhook-setup.md Connect to agent — Pass validated emails to your AI agent for processing Before You Start: Account & API Key Setup First Question: New or Existing Resend Account? Ask your human: New account just for the agent? → Simpler setup, full account access is fine Existing account with other projects? → Use domain-scoped API keys for sandboxing Creating API Keys Securely Don't paste API keys in chat! They'll be in conversation history forever. Safer options: Environment file method: Human creates .env file directly: echo "RESEND_API_KEY=re_xxx" >> .env Password manager / secrets manager: Human stores key in 1Password, Vault, etc. If key must be shared in chat: Human should rotate the key immediately after setup Domain-Scoped API Keys (Recommended for Existing Accounts) If your human has an existing Resend account with other projects, create a domain-scoped API key : Verify the agent's domain first (Dashboard → Domains → Add Domain) Create a scoped API key: Dashboard → API Keys → Create API Key → "Sending access" → select only the agent's domain Result: Even if the key leaks, it can only send from one domain Domain Setup Option 1: Resend-Managed Domain (Recommended for Getting Started) Use your auto-generated address: <anything>@<your-id>.resend.app No DNS configuration needed. Find your address in Dashboard → Emails → Receiving → "Receiving address". Option 2: Custom Domain The user must enable receiving in the Resend dashboard: Domains page → toggle on "Enable Receiving". Then add an MX record: Setting Value Type MX Host Your domain or subdomain (e.g., agent.example.com ) Value Provided in Resend dashboard Priority 10 (must be lowest number to take precedence) Use a subdomain (e.g., agent.example.com ) to avoid disrupting existing email services. Tip: Verify DNS propagation at dns.email . DNS Propagation: MX record changes can take up to 48 hours to propagate globally, though often complete within a few hours. Security Levels Choose your security level before setting up the webhook endpoint. An AI agent that processes emails without security is dangerous — anyone can email instructions that your agent will execute. The webhook code you write next should include your chosen security level from the start. Ask the user what level of security they want, and ensure that they understand what each level means. Level Name When to Use Trade-off 1 Strict Allowlist Most use cases — known, fixed set of senders Maximum security, limited functionality 2 Domain Allowlist Organization-wide access from trusted domains More flexible, anyone at domain can interact 3 Content Filtering Accept from anyone, filter unsafe patterns Can receive from anyone, pattern matching not foolproof 4 Sandboxed Processing Process all emails with restricted agent capabilities Maximum flexibility, complex to implement 5 Human-in-the-Loop Require human approval for untrusted actions Maximum security, adds latency For detailed implementation code for each level, see references/security-levels.md . Level 1: Strict Allowlist (Recommended) Only process emails from explicitly approved addresses. Reject everything else. const ALLOWED_SENDERS = [ 'you@youremail.com' , 'notifications@github.com' , ]; async function processEmailForAgent ( eventData : EmailReceivedEvent , emailContent : EmailContent ) { const sender = eventData. from . toLowerCase (); if (! ALLOWED_SENDERS . some ( allowed => sender === allowed. toLowerCase ())) { console . log ( `Rejected email from unauthorized sender: ${sender} ` ); await notifyOwnerOfRejectedEmail (eventData); return ; } await agent. processEmail ({ from : eventData. from , subject : eventData. subject , body : emailContent. text || emailContent. html , }); } Security Best Practices Always Do Practice Why Verify webhook signatures Prevents spoofed webhook events Log all rejected emails Audit trail for security review Use allowlists where possible Explicit trust is safer than filtering Rate limit email processing Prevents excessive processing load Separate trusted/untrusted handling Different risk levels need different treatment Never Do Anti-Pattern Risk Process emails without validation Anyone can control your agent Trust email headers for authentication Headers are trivially spoofed Execute code from email content Untrusted input should never run as code Store email content in prompts verbatim Untrusted input mixed into prompts can alter agent behavior Give untrusted emails full agent access Scope capabilities to the minimum needed Webhook Endpoint After choosing your security level and setting up your domain, create a webhook endpoint. The webhook endpoint MUST be a POST route. Resend sends all webhook events as POST requests. Critical: Use raw body for verification. Webhook signature verification requires the raw request body. Next.js App Router: Use req.text() (not req.json() ) Express: Use express.raw({ type: 'application/json' }) on the webhook route Next.js App Router // app/webhook/route.ts import { Resend } from 'resend' ; import { NextRequest , NextResponse } from 'next/server' ; const resend = new Resend (process. env . RESEND_API_KEY ); export async function POST ( req : NextRequest ) { try { const payload = await req. text (); const event = resend. webhooks . verify ({ payload, headers : { 'svix-id' : req. headers . get ( 'svix-id' ), 'svix-timestamp' : req. headers . get ( 'svix-timestamp' ), 'svix-signature' : req. headers . get ( 'svix-signature' ), }, secret : process. env . RESEND_WEBHOOK_SECRET , }); if (event. type === 'email.received' ) { // Webhook payload only includes metadata, not email body const { data : email } = await resend. emails . receiving . get ( event. data . email_id ); // Apply the security level chosen above await processEmailForAgent (event. data , email); } return new NextResponse ( 'OK' , { status : 200 }); } catch (error) { console . error ( 'Webhook error:' , error); return new NextResponse ( 'Error' , { status : 400 }); } } Express import express from 'express' ; import { Resend } from 'resend' ; const app = express (); const resend = new Resend (process. env . RESEND_API_KEY ); const ALLOWED_SENDERS = (process. env . ALLOWED_SENDERS || '' ). split ( ',' ). filter ( Boolean ); const isAllowedSender = ( sender ) => ALLOWED_SENDERS . some ( allowed => sender === allowed. toLowerCase ()); app. post ( '/webhook' , express. raw ({ type : 'application/json' }), async (req, res) => { try { const payload = req. body . toString (); const event = resend. webhooks . verify ({ payload, headers : { 'svix-id' : req. headers [ 'svix-id' ], 'svix-timestamp' : req. headers [ 'svix-timestamp' ], 'svix-signature' : req. headers [ 'svix-signature' ], }, secret : process. env . RESEND_WEBHOOK_SECRET , }); if (event. type === 'email.received' ) { const sender = event. data . from . toLowerCase (); if (! isAllowedSender (sender)) { console . log ( `Rejected email from unauthorized sender: ${sender} ` ); res. status ( 200 ). send ( 'OK' ); // Return 200 even for rejected emails return ; } const { data : email } = await resend. emails . receiving . get (event. data . email_id ); await processEmailForAgent (event. data , email); } res. status ( 200 ). send ( 'OK' ); } catch (error) { console . error ( 'Webhook error:' , error); res. status ( 400 ). send ( 'Error' ); } }); app. get ( '/' , ( req, res ) => res. send ( 'Agent Email Inbox - Ready' )); app. listen ( 3000 , () => console . log ( 'Webhook server running on :3000' )); For webhook registration via API, tunneling setup, svix fallback, and retry behavior, see references/webhook-setup.md . Sending Emails from Your Agent import { Resend } from 'resend' ; const resend = new Resend (process. env . RESEND_API_KEY ); async function sendAgentReply ( to : string , subject : string , body : string , inReplyTo ?: string ) { if (! isAllowedToReply (to)) { throw new Error ( 'Cannot send to this address' ); } const { data, error } = await resend. emails . send ({ from : 'Agent <agent@example.com>' , to : [to], subject : subject. startsWith ( 'Re:' ) ? subject : `Re: ${subject} ` , text : body, headers : inReplyTo ? { 'In-Reply-To' : inReplyTo } : undefined , }); if (error) throw new Error ( `Failed to send: ${error.message} ` ); return data. id ; } For full sending docs, install the resend skill. Environment Variables # Required RESEND_API_KEY=re_xxxxxxxxx RESEND_WEBHOOK_SECRET=whsec_xxxxxxxxx # Security Configuration SECURITY_LEVEL=strict # strict | domain | filtered | sandboxed ALLOWED_SENDERS=you@email.com,trusted@example.com ALLOWED_DOMAINS=example.com OWNER_EMAIL=you@email.com # For security notifications Common Mistakes Mistake Fix No sender verification Always validate who sent the email before processing Trusting email headers Use webhook verification, not email headers for auth Same treatment for all emails Differentiate trusted vs untrusted senders Verbose error messages Keep error responses generic to avoid leaking internal logic No rate limiting Implement per-sender rate limits. See references/advanced-patterns.md Processing HTML directly Strip HTML or use text-only to reduce complexity and risk No logging of rejections Log all security events for audit Using ephemeral tunnel URLs Use persistent URLs (Tailscale Funnel, paid ngrok) or deploy to production Using express.json() on webhook route Use express.raw({ type: 'application/json' }) — JSON parsing breaks signature verification Returning non-200 for rejected emails Always return 200 to acknowledge receipt — otherwise Resend retries Old Resend SDK version emails.receiving.get() and webhooks.verify() require recent SDK versions — see SDK Version Requirements Testing Use Resend's test addresses for development: delivered@resend.dev — Simulates successful delivery bounced@resend.dev — Simulates hard bounce For security testing, send test emails from non-allowlisted addresses to verify rejection works correctly. Quick verification checklist: Server is running: curl http://localhost:3000 should return a response