How do API outages or webhook lag create data gaps?
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When you're pulling engagement data from your ESP via API or receiving it through webhooks, you're depending on a real-time connection. When that connection has problems, your data gets holes in it. The gaps aren't always obvious, and they can quietly corrupt analysis you've trusted for days before anyone notices.
What API outages do to your data
If your system polls the ESP API on a schedule (say, every 15 minutes) and the API is down or slow during one of those windows, that window's events don't get recorded. If you're running your own database, those events may be missed permanently unless your integration has retry logic. A campaign that sent at 10am with the API down from 10:15 to 11:00 could be missing 45 minutes of open and click events. Your open rate for that campaign shows lower than reality.
What webhook lag does
Webhooks are supposed to deliver events in near real time. But ESP webhook delivery isn't guaranteed to be instantaneous or in order. During high-volume sends, events can queue up on the ESP's side and arrive delayed. You might process a click event before the corresponding open event. Or an unsubscribe arrives before the open that preceded it.
Out-of-order events cause logic errors if your system expects sequential event data. A click registered before an open looks like a bot signal to filters that check event order. An unsubscribe processed before an open can corrupt contact state if your system doesn't handle sequence gaps.
How to protect against it
For API polling: build retry logic that re-fetches any window that returned an error or timed out. For webhooks: use a queue system (like an event queue or message broker) that accepts events in any order and processes them correctly. Most reliable webhook implementations use an idempotency key so duplicate events (common in retry scenarios) don't create duplicate records.
If you're seeing inconsistencies in your campaign data that don't match what your ESP's own dashboard shows, data gaps from outages or lag are a likely culprit.
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