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Use when sending transactional emails (welcome messages, order confirmations, password resets, receipts), notifications, or bulk emails via Resend API.
默认使用会先检查来源的 Prompt；你也可以切换为直接命令，或下载本地副本。
决定是否安装前，请先阅读 SKILL.md，以及 SkillsMP 当前展示的配套文件。
用 Codex 或 Claude 帮你安装 复制这段 Prompt，粘贴到 Codex、Claude 或其他助手里，让它检查 Skill 页面并帮你完成安装。
直接命令不会经过审查 Prompt；运行前请先检查来源。
npx skills add https://github.com/Nexprove-Team/hykehyre --skill send-email命令会保持在同一行。复制前请横向滚动并检查完整内容。
想先保存到本地？可下载 SkillsMP 当前能够提供的文件。
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| name | send-email |
| description | Use when sending transactional emails (welcome messages, order confirmations, password resets, receipts), notifications, or bulk emails via Resend API. |
Resend provides two endpoints for sending emails:
| Approach | Endpoint | Use Case |
|---|---|---|
| Single | POST /emails | Individual transactional emails, emails with attachments, scheduled sends |
| Batch | POST /emails/batch | Multiple distinct emails in one request (max 100), bulk notifications |
Choose batch when:
Choose single when:
Always implement these for production email sending. See references/best-practices.md for complete implementations.
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 |
| Duplicate payload | Returns original response without resending |
| Different payload | Returns 409 error |
| Code | Action |
|---|---|
| 400, 422 | Fix request parameters, don't retry |
| 401, 403 | Check API key / verify domain, don't retry |
| 409 | Idempotency conflict - use new key or fix payload |
| 429 | Rate limited - retry with exponential backoff (by default, rate limit is 2 requests/second) |
| 500 | Server error - retry with exponential backoff |
Endpoint: POST /emails (prefer SDK over cURL)
| Parameter | Type | Description |
|---|---|---|
from | string | Sender address. Format: "Name <email@domain.com>" |
to | string[] | Recipient addresses (max 50) |
subject | string | Email subject line |
html or text | string | Email body content |
| Parameter | Type | Description |
|---|---|---|
cc | string[] | CC recipients |
bcc | string[] | BCC recipients |
reply_to* | string[] | Reply-to addresses |
scheduled_at* | string | Schedule send time (ISO 8601) |
attachments | array | File attachments (max 40MB total) |
tags | array | Key/value pairs for tracking (see Tags) |
headers | object | Custom headers |
*Parameter naming varies by SDK (e.g., replyTo in Node.js, reply_to in Python).
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/${userId}` },
);
if (error) {
console.error("Failed:", error.message);
return;
}
console.log("Sent:", data.id);
See references/single-email-examples.md for all SDK implementations with error handling and retry logic.
Endpoint: POST /emails/batch (but prefer SDK over cURL)
Since the entire batch fails on any validation error, validate all emails before sending:
import { Resend } from "resend";
const resend = new Resend(process.env.RESEND_API_KEY);
const { data, error } = await resend.batch.send(
[
{
from: "Acme <notifications@acme.com>",
to: ["delivered@resend.dev"],
subject: "Order Shipped",
html: "<p>Your order has shipped!</p>",
},
{
from: "Acme <notifications@acme.com>",
to: ["delivered@resend.dev"],
subject: "Order Confirmed",
html: "<p>Your order is confirmed!</p>",
},
],
{ idempotencyKey: `batch-orders/${batchId}` },
);
if (error) {
console.error("Batch failed:", error.message);
return;
}
console.log(
"Sent:",
data.map((e) => e.id),
);
See references/batch-email-examples.md for all SDK implementations with validation, error handling, and retry logic.
For sends larger than 100 emails, chunk into multiple batch requests:
<batch-prefix>/chunk-<index>See references/batch-email-examples.md for complete chunking implementations.
Follow these practices to maximize inbox placement.
For more help with deliverability, install the email-best-practices skill with npx skills add resend/email-best-practices.
| Practice | Why |
|---|---|
| Valid SPF, DKIM, DMARC record | authenticate the email and prevent spoofing |
| Links match sending domain | If sending from @acme.com, link to https://acme.com - mismatched domains trigger spam filters |
| Include plain text version | Use both html and text parameters for accessibility and deliverability (Resend generates a plain text version if not provided) |
| Avoid "no-reply" addresses | Use real addresses (e.g., support@) - improves trust signals |
| Keep body under 102KB | Gmail clips larger messages |
| Practice | Why |
|---|---|
| Use subdomains | Send transactional from notifications.acme.com, marketing from mail.acme.com - protects reputation |
| Disable tracking for transactional | Open/click tracking can trigger spam filters for password resets, receipts, etc. |
Tracking is configured at the domain level in the Resend dashboard, not per-email.
| Setting | How it works | Recommendation |
|---|---|---|
| Open tracking | Inserts 1x1 transparent pixel | Disable for transactional emails - can hurt deliverability |
| Click tracking | Rewrites links through redirect | Disable for sensitive emails (password resets, security alerts) |
When to enable tracking:
When to disable tracking:
Configure via dashboard: Domain → Configuration → Click/Open Tracking
Track email delivery status in real-time using webhooks. Resend sends HTTP POST requests to your endpoint when events occur.
| Event | When to use |
|---|---|
email.delivered | Confirm successful delivery |
email.bounced | Remove from mailing list, alert user |
email.complained | Unsubscribe user (spam complaint) |
email.opened / email.clicked | Track engagement (marketing only) |
CRITICAL: Always verify webhook signatures. Without verification, attackers can send fake events to your endpoint.
See references/webhooks.md for setup, signature verification code, and all event types.
Tags are key/value pairs that help you track and filter emails.
tags: [
{ name: "user_id", value: "usr_123" },
{ name: "email_type", value: "welcome" },
{ name: "plan", value: "enterprise" },
];
Use cases:
Constraints: Tag names and values can only contain ASCII letters, numbers, underscores, or dashes. Max 256 characters each.
Use pre-built templates instead of sending HTML with each request.
const { data, error } = await resend.emails.send({
from: "Acme <hello@acme.com>",
to: ["delivered@resend.dev"],
subject: "Welcome!",
template: {
id: "tmpl_abc123",
variables: {
USER_NAME: "John", // Case-sensitive!
ORDER_TOTAL: "$99.00",
},
},
});
IMPORTANT: Variable names are case-sensitive and must match exactly as defined in the template editor. USER_NAME ≠ user_name.
| Fact | Detail |
|---|---|
| Max variables | 20 per template |
| Reserved names | FIRST_NAME, LAST_NAME, EMAIL, RESEND_UNSUBSCRIBE_URL, contact, this |
| Fallback values | Optional - if not set and variable missing, send fails |
| Can't combine with | html, text, or react parameters |
Templates must be published in the dashboard before use. Draft templates won't work.
WARNING: Never test with fake addresses at real email providers.
Using addresses like test@gmail.com, example@outlook.com, or fake@yahoo.com will:
| Method | Address | Result |
|---|---|---|
| Delivered | delivered@resend.dev | Simulates successful delivery |
| Bounced | bounced@resend.dev | Simulates hard bounce |
| Complained | complained@resend.dev | Simulates spam complaint |
| Your own email | Your actual address | Real delivery test |
For development: Use the resend.dev test addresses to simulate different scenarios without affecting your reputation.
For staging: Send to real addresses you control (team members, test accounts you own).
New domains must gradually increase sending volume to establish reputation.
Why it matters: Sudden high volume from a new domain triggers spam filters. ISPs expect gradual growth.
Existing domain
| Day | Messages per day | Messages per hour |
|---|---|---|
| 1 | Up to 1,000 emails | 100 Maximum |
| 2 | Up to 2,500 emails | 300 Maximum |
| 3 | Up to 5,000 emails | 600 Maximum |
| 4 | Up to 5,000 emails | 800 Maximum |
| 5 | Up to 7,500 emails | 1,000 Maximum |
| 6 | Up to 7,500 emails | 1,500 Maximum |
| 7 | Up to 10,000 emails | 2,000 Maximum |
New domain
| Day | Messages per day | Messages per hour |
|---|---|---|
| 1 | Up to 150 emails | |
| 2 | Up to 250 emails | |
| 3 | Up to 400 emails | |
| 4 | Up to 700 emails | 50 Maximum |
| 5 | Up to 1,000 emails | 75 Maximum |
| 6 | Up to 1,500 emails | 100 Maximum |
| 7 | Up to 2,000 emails | 150 Maximum |
| Metric | Target | Action if exceeded |
|---|---|---|
| Bounce rate | < 4% | Slow down, clean list |
| Spam complaint rate | < 0.08% | Slow down, review content |
Don't use third-party warm-up services. Focus on sending relevant content to real, engaged recipients.
Resend automatically manages a suppression list of addresses that should not receive emails.
Addresses are added when:
What happens: Resend won't attempt delivery to suppressed addresses. The email.suppressed webhook event fires instead.
Why this matters: Continuing to send to bounced/complained addresses destroys your reputation. The suppression list protects you automatically.
Management: View and manage suppressed addresses in the Resend dashboard under Suppressions.
| Mistake | Fix |
|---|---|
| Retrying without idempotency key | Always include idempotency key - prevents duplicate sends on retry |
| Using batch for emails with attachments | Batch doesn't support attachments - use single sends instead |
| Not validating batch before send | Validate all emails first - one invalid email fails the entire batch |
| Retrying 400/422 errors | These are validation errors - fix the request, don't retry |
| Same idempotency key, different payload | Returns 409 error - use unique key per unique email content |
| Tracking enabled for transactional emails | Disable open/click tracking for password resets, receipts - hurts deliverability |
| Using "no-reply" sender address | Use real address like support@ - improves trust signals with email providers |
| Not verifying webhook signatures | Always verify - attackers can send fake events to your endpoint |
| Testing with fake emails (test@gmail.com) | Use delivered@resend.dev - fake addresses bounce and hurt reputation |
| Template variable name mismatch | Variable names are case-sensitive - USER_NAME ≠ user_name |
| Sending high volume from new domain | Warm up gradually - sudden spikes trigger spam filters |
from address must use a verified domainreply_to parameter to a valid address.RESEND_API_KEY environment variablereact parameter for React Email componentserror, data, headers in the response.{ id: "email-id" } on success (single) or array of IDs (batch)