Usage limit warnings

Your app knows a customer is close to their plan limit on every request that counts towards it. That is exactly where you want to warn them, and exactly why a plain send would email them hundreds of times a day.

With delivery.throttle you send from that hot path anyway. Plunk delivers the warning once per window and skips the rest, so your app keeps no record of who was warned when.

Setup

Subject: You've used {{percent}}% of your {{plan}} plan

Hi {{firstName}}, {{organisation}} has used {{used}} of its {{limit}} emails this month.
Upgrade before you reach the limit to keep sending without interruption.

async function recordUsage(org, user) {
  const used = await incrementUsage(org.id);
  const percent = Math.floor((used / org.limit) * 100);

  if (percent >= 80) {
    await fetch('https://next-api.useplunk.com/v1/send', {
      method: 'POST',
      headers: {
        Authorization: `Bearer ${process.env.PLUNK_SECRET_KEY}`,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({
        to: user.email,
        template: process.env.PLUNK_USAGE_WARNING_TEMPLATE,
        data: {percent, used, limit: org.limit, plan: org.plan, organisation: org.name},
        delivery: {throttle: {window: '24h', key: org.id}},
      }),
    });
  }
}

Variations

Once per billing period instead of once a day. Drop the window and put the period in the key. The warning goes out once, and the new key next month lets it go out again:

{ "delivery": { "throttle": { "key": "org_123:2026-10" } } }

One warning per threshold. Use a different key for 80% and 100%, so crossing the second threshold still sends even if the first went out an hour ago:

{ "delivery": { "throttle": { "window": "24h", "key": "org_123:100" } } }

Tell the whole team, once. Send to every admin with scope: "project" and the first one who triggers it gets the email, while nobody is told twice within the window. More often you want each admin told, which is the default.

Without code

Prefer to keep the email in a workflow? Track an event where the usage is counted and let the workflow throttle itself:

await fetch('https://next-api.useplunk.com/v1/track', {
  method: 'POST',
  headers: {
    Authorization: `Bearer ${process.env.PLUNK_SECRET_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    event: 'usage.high',
    email: user.email,
    data: {orgId: org.id, percent, used, limit: org.limit},
  }),
});

Then create a workflow triggered by usage.high with a Send email step, and under Who can enter pick At most once per period: every 24 hours, counted separately for each event.orgId. Every tracked event is stored as usual, but only the first one per organisation per day starts the workflow.