resend

name resend description Use when working with the Resend email API — sending transactional emails (single or batch), receiving inbound emails via webhooks, managing email templates, tracking delivery events, managing domains, contacts, broadcasts, webhooks, API keys, automations, events, viewing API request logs, or setting up the Resend SDK. Always use this skill when the user mentions Resend, even for simple tasks like "send an email with Resend" — the skill contains critical gotchas (idempotency keys, webhook verification, template variable syntax) that prevent common production issues. license MIT metadata {"author":"resend","version":"3.8.0","homepage":"https://resend.com/agent-skills","source":"https://github.com/resend/resend-skills","openclaw":{"primaryEnv":"RESEND_API_KEY","requires":{"env":"[Truncated]"},"envVars":["[Truncated]","[Truncated]"],"links":{"repository":"https://github.com/resend/resend-skills","documentation":"https://resend.com/docs/resend-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 event payloads. Found in the Resend dashboard under Webhooks after creating an endpoint.","required":false}] references ["sending","receiving.md","templates.md","webhooks.md","domains.md","contacts.md","broadcasts.md","api-keys.md","logs.md","contact-properties.md","segments.md","topics.md","automations.md","events.md","installation.md","fetch-all-templates.mjs"] Resend Quick Send — Node.js import { Resend } from 'resend' ; const resend = new Resend (process. env . RESEND_API_KEY ); const { data, error } = await resend. emails . send ( { from : 'Acme <onboarding@resend.dev>' , to : [ 'delivered@resend.dev' ], subject : 'Hello World' , html : '<p>Email body here</p>' , }, { idempotencyKey : `welcome-email/ ${userId} ` } ); if (error) { console . error ( 'Failed:' , error. message ); return ; } console . log ( 'Sent:' , data. id ); Key gotcha: The Resend Node.js SDK does NOT throw exceptions — it returns { data, error } . Always check error explicitly instead of using try/catch for API errors. Quick Send — Python import resend import os resend.api_key = os.environ[ "RESEND_API_KEY" ] email = resend.Emails.send({ "from" : "Acme <onboarding@resend.dev>" , "to" : [ "delivered@resend.dev" ], "subject" : "Hello World" , "html" : "<p>Email body here</p>" , }, idempotency_key= f"welcome-email/ {user_id} " ) Single vs Batch Decision Choose When Single ( POST /emails ) 1 email, needs attachments, needs scheduling Batch ( POST /emails/batch ) 2-100 distinct emails, no attachments, no scheduling Batch is atomic — if one email fails validation, the entire batch fails. Always validate before sending. Batch does NOT support attachments or scheduled_at . Idempotency Keys (Critical for Retries) Prevent duplicate emails when retrying failed requests: Key Facts Format (single) <event-type>/<entity-id> (e.g., welcome-email/user-123 ) Format (batch) batch-<event-type>/<batch-id> (e.g., batch-orders/batch-456 ) Expiration 24 hours Max length 256 characters Same key + same payload Returns original response without resending Same key + different payload Returns 409 error Quick Receive (Node.js) import { Resend } from 'resend' ; const resend = new Resend (process. env . RESEND_API_KEY ); export async function POST ( req : Request ) { const payload = await req. text (); // Must use raw text, not req.json() 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 has metadata only — call API for body const { data : email } = await resend. emails . receiving . get ( event. data . email_id ); console . log (email. text ); } return new Response ( 'OK' , { status : 200 }); } Key gotcha: Webhook payloads do NOT contain the email body. You must call resend.emails.receiving.get() separately. What Do You Need? Task Reference Send a single email sending/overview.md — parameters, deliverability, testing Send batch emails sending/overview.md → sending/batch-email-examples.md Full SDK examples (Node.js, Python, Go, cURL) sending/single-email-examples.md Idempotency, retries, error handling sending/best-practices.md Get, list, reschedule, cancel emails, retrieve metrics sending/email-management.md Receive inbound emails receiving.md — domain setup, webhooks, attachments Manage templates (CRUD, variables) templates.md — lifecycle, aliases, pagination Set up webhooks (events, verification) webhooks.md — verification, CRUD, retry schedule, IP allowlist Manage domains (create, verify, claim, DNS) domains.md — regions, TLS, tracking, claiming, capabilities Manage contacts (CRUD, properties) contacts.md — segments, topics, custom properties, bulk CSV import Send broadcasts (marketing campaigns) broadcasts.md — lifecycle, scheduling, template variables Manage API keys api-keys.md — permission scoping, domain restrictions View API request logs logs.md — list and retrieve API call history, debugging Define contact properties contact-properties.md — custom fields for contacts Manage segments (contact groups) segments.md — broadcast targeting, contact grouping Manage topics (subscriptions) topics.md — opt-in/out preferences, broadcast filtering Create automations (event-driven workflows) automations.md — steps, connections, runs, conditions Define and send events (automation triggers) events.md — schemas, payloads, contact association Install SDK (8+ languages) installation.md Set up an AI agent inbox Install the agent-email-inbox skill — covers security levels for untrusted input SDK Version Requirements Always install the latest SDK version. These are the minimum versions for full functionality (sending, receiving, webhook verification): Language Package Min Version Install Node.js resend >= 6.14.0 npm install resend Python resend >= 2.34.0 pip install resend Go resend-go/v3 >= 3.11.0 go get github.com/resend/resend-go/v3 Ruby resend >= 1.6.0 gem install resend PHP resend/resend-php >= 1.1.0 composer require resend/resend-php Rust resend-rs >= 0.26.1 cargo add resend-rs Java resend-java >= 4.16.0 See installation.md .NET Resend >= 0.2.1 dotnet add package Resend If the project already has a Resend SDK installed , check the version and upgrade if it's below the minimum. Older SDKs may be missing webhooks.verify() , emails.receiving.get() , or domains.claims.* . See installation.md for full installation commands, language detection, and cURL fallback. Common Setup API Key Store in environment variable — never hardcode: export RESEND_API_KEY=re_xxxxxxxxx Get your key at resend.com/api-keys . Detect Project Language Check for these files: package.json (Node.js), requirements.txt / pyproject.toml (Python), go.mod (Go), Gemfile (Ruby), composer.json (PHP), Cargo.toml (Rust), pom.xml / build.gradle (Java), *.csproj (.NET). Common Mistakes # Mistake Fix 1 Retrying without idempotency key Always include idempotency key — prevents duplicate sends on retry. Format: <event-type>/<entity-id> 2 Not verifying webhook signatures Always verify with resend.webhooks.verify() — unverified events can't be trusted 3 Template variable name mismatch Variable names are case-sensitive — must match the template definition exactly. Use triple mustache {{{VAR}}} syntax 4 Expecting email body in webhook payload Webhooks contain metadata only — call resend.emails.receiving.get() for body content 5 Using try/catch for Node.js SDK errors SDK returns { data, error } — check error explicitly, don't wrap in try/catch 6 Using batch for emails with attachments Batch doesn't support attachments — use single sends instead 7 Testing with fake emails ( test@gmail.com ) Use delivered@resend.dev — fake addresses bounce and hurt reputation 8 Sending with draft template Templates must be published before sending — call .publish() first 9 html + template in same send call Mutually exclusive — remove html / text / react when using template 10 MX record not lowest priority for inbound Ensure Resend's MX has the lowest number (highest priority) or emails won't route 11 403 when sending from resend.dev The default onboarding@resend.dev is a sandbox — it can only deliver to your Resend account email. Verify your own domain first 12 403 domain mismatch The from address domain must exactly match a verified domain. Verified send.acme.com but sending from user@acme.com will fail 13 Calling Resend API from the browser (CORS) The API does not support CORS — this is intentional to protect your API key. Always call from server-side (API routes, serverless functions) 14 401 restricted_api_key A sending-only API key was used on a non-sending endpoint (domains, contacts, etc.). Create a full-access key instead Cross-Cutting Concerns Send + Receive Together Auto-replies, email forwarding, or any receive-then-send workflow requires both capabilities: Set up inbound domain first (see receiving.md ) Set up sending (see sending/overview.md ) Note: batch sending does NOT support attachments or scheduling — use single sends when forwarding with attachments AI Agent Inbox If your system processes untrusted email content and takes actions (refunds, database changes, forwarding), install the agent-email-inbox skill. This applies whether or not AI is involved — any system interpreting freeform email content from external senders needs security measures. Marketing Emails The sending capabilities in this skill are for transactional email (receipts, confirmations, notifications). For marketing campaigns to large subscriber lists with unsubscribe links and engagement tracking, use Resend Broadcasts — see broadcasts.md for the API. Domain Warm-up New domains must gradually increase sending volume. Day 1 limit: ~150 emails (new domain) or ~1,000 (existing domain). See the warm-up schedule in sending/overview.md . Testing Never test with fake addresses at real email providers ( test@gmail.com , fake@outlook.com ) — they bounce and destroy sender reputation. Address Result delivered@resend.dev Simulates successful delivery bounced@resend.dev Simulates hard bounce complained@resend.dev Simulates spam complaint Suppression List Resend automatically suppresses hard-bounced and spam-complained addresses. Sending to suppressed addresses fires the email.suppressed webhook event instead of attempting delivery. Manage in Dashboard → Suppressions. Webhook Event Types Event Trigger email.sent API request successful email.delivered Reached recipient's mail server email.bounced Permanently rejected (hard bounce) email.complained Recipient marked as spam email.opened / email.clicked Recipient engagement email.delivery_delayed Soft bounce, Resend retries email.received Inbound email arrived domain.* / contact.* Domain/contact changes See webhooks.md for full details, signature verification, and retry schedule. Error Handling Quick Reference | Code | Action |