What’s a trigger loop?
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Imagine you build a welcome automation. It fires when someone joins your list, sends a warm first email, then tags them as "welcomed" in your CRM. Sounds clean. But what if your CRM update also counts as a profile change event, and your profile change automation fires a second welcome email? And that second email updates a field that triggers the first automation again?
That's a trigger loop. Two automations keep firing each other, and the only thing your subscriber experiences is their inbox filling up fast.
Loops are sneaky because each individual automation looks perfectly reasonable when you review it in isolation. The problem only shows up when they interact. A welcome flow, an overlap in automation conditions, a CRM sync event, an ESP callback, all fine on their own. Together, they create a circular chain with no exit.
A few patterns that show up most often:
- A welcome email triggers an engagement automation, which sends a welcome variant, which re-triggers the engagement automation.
- A CRM field update fires an automation in your ESP. The ESP sends an email, logs the event, and pushes that event back to the CRM, which updates the field again.
- A "re-engagement" flow marks a subscriber as active after a click. That active status triggers a new onboarding sequence that marks them as a new contact. Loop.
The fastest way to catch these before they cause damage is to map your automation triggers visually before going live. Draw out every trigger, every action, and every output. If any output can become a trigger anywhere else in the system, you need an exit rule. That means setting maximum iteration limits, using unique event IDs so the same event can't fire twice, or adding a suppression tag that prevents re-entry once a contact has already been through a flow.
If you're already dealing with missing suppression logic, you're more vulnerable to loops than you might think. Suppression rules are often the only thing standing between a clean automation and a runaway one.
If something has already gone wrong and a loop is running right now, pause every automation touching that contact segment first. Then trace the chain. Don't try to fix it while it's firing.
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