Sending new post notifications with Resend

When a new post goes live, I want subscribers to know about it. The mailing list runs through Resend — subscribers are stored in a Resend Segment, and broadcasting to them means calling the Resend Broadcasts API. The question was: how do I trigger that broadcast as part of the publish flow, without adding complexity to the build pipeline?

The answer is a standalone Node.js script — scripts/notify-new-post.js — that runs manually after publishing. It reads frontmatter directly, builds an HTML email, previews it in the terminal, and asks for confirmation before sending.

Why a script rather than a build hook

There are a few reasons.

A build hook would run on every deploy, including deploys for unrelated changes like CSS fixes or draft work. Broadcasts should only happen for new public posts — triggering them from the build process would require additional logic to detect whether anything post-worthy had actually changed, which gets complicated quickly.

Running the script manually is intentional friction. It forces a moment of review before an email goes out to every subscriber. That’s the right default.

Dependencies

The script uses one external dependency: @inquirer/prompts for interactive select and confirmation prompts. Everything else is Node.js built-ins — readFileSync, readdirSync, path utilities. No Astro, no Zod, no content collections.

Reading frontmatter without a build

The script includes a minimal frontmatter parser rather than pulling in a YAML library:

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function parseFrontmatter(content) {
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  const match = content.match(/^---\r?\n([\s\S]*?)\r?\n---/);
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  if (!match) return {};
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  const yaml = match[1];
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  const result = {};
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  for (const line of yaml.split(/\r?\n/)) {
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    const m = line.match(/^(\w+):\s*["'>]?(.*?)["']?\s*$/);
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    if (m) result[m[1]] = m[2].trim();
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  }
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  // Handle YAML block scalar for description (>- or >)
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  const descBlock = yaml.match(/^description:\s*>-?\r?\n((?:[ \t]+.+\r?\n?)*)/m);
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  if (descBlock) {
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    result.description = descBlock[1]
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      .split(/\r?\n/)
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      .map((l) => l.trim())
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      .filter(Boolean)
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      .join(" ");
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  }
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  return result;
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}

This only handles simple key: value lines and the >- block scalar for description. It’s intentionally minimal — the script doesn’t need to parse the full YAML AST.

The listPostIds function finds posts published in the past week that aren’t drafts. Each directory read is wrapped in a try/catch so unreadable or malformed posts are silently skipped rather than crashing the script:

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function listPostIds() {
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  const postsDir = join(root, "collections", "posts");
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  const oneWeekAgo = Date.now() - 7 * 24 * 60 * 60 * 1000;
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  return readdirSync(postsDir, { withFileTypes: true })
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    .filter((d) => d.isDirectory())
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    .map((d) => {
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      try {
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        const content = readFileSync(join(postsDir, d.name, "index.md"), "utf8");
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        const fm = parseFrontmatter(content);
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        const pubDate = fm.pubDate ? new Date(fm.pubDate).getTime() : 0;
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        const isDraft = fm.draft === "true";
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        return { id: d.name, pubDate, isDraft };
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      } catch {
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        return null;
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      }
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    })
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    .filter((p) => p && !p.isDraft && p.pubDate >= oneWeekAgo)
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    .sort((a, b) => b.pubDate - a.pubDate)
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    .map((p) => p.id);
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}

Environment variables

The script reads secrets from a .env file in the project root (using Node 20.12’s process.loadEnvFile) or from shell environment variables — shell variables take precedence:

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const envFile = join(root, ".env");
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if (existsSync(envFile)) {
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  if (typeof process.loadEnvFile === "function") {
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    process.loadEnvFile(envFile);
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  }
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}

Required variables:

• RESEND_API_KEY — Resend API key with broadcast send permissions
• RESEND_SEGMENT_ID — the Segment ID to broadcast to
• SITE_URL — base URL used to construct post links (defaults to https://sourcier.uk)

Optional variables:

• NOTIFY_FROM_EMAIL — the From: address in the broadcast (defaults to Roger @ Sourcier <hello@sourcier.uk>)
• RESEND_TOPIC_ID — if set, attaches a topic to the broadcast for unsubscribe granularity

The email content

The broadcast is sent with both an HTML body and a plain-text fallback. Email clients that can’t render HTML receive the plain-text version; everything else gets the styled one.

The HTML is built as an inline-styled string. Email clients don’t support external stylesheets or CSS custom properties — everything needs to be inline and use safe font stacks:

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function buildHtml() {
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  return `
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<div style="font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',sans-serif;max-width:560px;margin:0 auto;padding:2rem 1.5rem;color:#0f0f0f">
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  <p style="margin:0 0 1.5rem;line-height:1.6">Hi — I just published something new on Sourcier.</p>
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  <p style="font-size:1.5rem;font-weight:800;letter-spacing:-0.01em;margin:0 0 1rem;line-height:1.2">${title}</p>
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  ${excerpt ? `<p style="margin:0 0 1.5rem;line-height:1.6;color:#444">${excerpt}</p>` : ""}
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  <a href="${url}" style="display:inline-block;background:#e8006a;color:#fff;text-decoration:none;padding:0.65rem 1.5rem;font-weight:700;font-size:0.875rem;letter-spacing:0.04em;text-transform:uppercase">Read the post →</a>
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  <p style="margin:1.5rem 0 0;line-height:1.6;color:#444">If it sparks any thoughts, I'd love to hear them — there's a comments section at the bottom of the post.</p>
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  <p style="margin:1rem 0 0;line-height:1.6">— Roger</p>
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  <hr style="margin:2rem 0;border:none;border-top:1px solid #e5e5e5">
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  <p style="margin:0;color:#999;font-size:0.8125rem;line-height:1.5">
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    You're receiving this because you subscribed at sourcier.uk.<br>
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    <a href="{{{RESEND_UNSUBSCRIBE_URL}}}" style="color:#999">Unsubscribe</a>
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  </p>
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</div>`.trim();
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}

The {{{RESEND_UNSUBSCRIBE_URL}}} placeholder is Resend’s broadcast template variable — it’s replaced at send time with a personalised unsubscribe link for each recipient. It’s required by anti-spam regulations (CAN-SPAM, GDPR).

Confirmation before sending

The script uses @inquirer/prompts for both the post selection and the send confirmation. After printing the preview, it asks:

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const shouldSend = await confirm({
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  message: "Send this to all subscribers?",
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  default: false,
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});
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if (!shouldSend) {
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  console.log("Aborted — nothing was sent.");
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  process.exit(0);
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}

The default is false, so pressing Enter without typing y aborts safely.

If the post has draft: true in its frontmatter, the script surfaces a warning and asks a second confirmation before continuing. It doesn’t block sending outright — there are legitimate reasons to test-send a draft — but it makes the state explicit.

The two-step API call

Sending a broadcast is two separate calls to the Resend API. The first creates the broadcast and returns an ID:

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const createRes = await fetch(`${RESEND_API}/broadcasts`, {
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  method: "POST",
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  headers: { Authorization: `Bearer ${apiKey}`, "Content-Type": "application/json" },
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  body: JSON.stringify({ name: title, from: FROM, subject: SUBJECT, html, text, segment_id: segmentId }),
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});
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const { id } = await createRes.json();

The second dispatches it to the segment:

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await fetch(`${RESEND_API}/broadcasts/${id}/send`, {
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  method: "POST",
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  headers: { Authorization: `Bearer ${apiKey}` },
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});

Separating creation from dispatch is useful — it means the broadcast exists in the Resend dashboard before it’s sent, so you can inspect or cancel it if something looks wrong.

Running the script

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node scripts/notify-new-post.js

The script lists posts published in the past week, prompts to select one, shows a preview, and waits for confirmation. Pass --debug to log the full API request payload and response status to the terminal without sending anything.

Total runtime is a few seconds.

The approach here is deliberately low-tech: no build integration, no CI step, no webhook. A standalone script with a confirmation prompt is the right level of automation for something that goes out to every subscriber. The friction is the feature.

The full script is in the sourcier.uk repository.