How to Back-Populate a Flow
To back-populate a flow, click on the Flows tab, and then on the name of the flow from the list. Click on the Manage Flow dropdown in the header and click Back-Populate Flow Recipients.
The back-populate feature allows you to queue people for one or more flow emails retroactively. This is useful after you create a flow with emails scheduled in the future who would've been queued had the flow existed earlier.
For example, when you create customer a re-engagement flow, you probably don't want to wait 60 or 120 days for customers start receiving emails. Back-populating a flow will find customers who placed an order months ago and queue them for emails as soon as the next day.
Who is queued when you back-populate a flow depends on whether your flow trigger is a metric, list or segment and the sending status of your flow emails.
Emails will only be queued for flow emails whose sending status is manual or live.
How a List or Segment-Based Flow is Back-Populated
For flows triggered by a list or segment, everyone in the list or segment who has not been queued for that email will be queued.
Each person will be queued as if they had been added to the list or segment the day you click Back-Populate, not relative to the date they were added to the list.
For example, if a flow sends an email after 30 days and someone subscribed on January 1, back-populating the flow on March 1 would schedule them to receive that email on March 31. If a different person subscribed on January 15, they would also be scheduled to receive the email on March 31.
How an Event-Based Flow is Back-Populated
For flows triggered by an event (for example, Placed Order), emails will be queued relative when a recipient triggered a flow, and only for people who would be scheduled to receive that email within the time parameters of the flow. Because emails that are past due aren't sent, any emails timed to send immediately won't back-populate.
For example, if a flow is triggered by someone placing an order and sends an email after 30 days, back-populating the flow on January 1 would schedule emails for anyone who placed an order between December 2 and January 1. If someone placed an order on December 3, they would be scheduled to receive an email on January 2. If another customer placed an order on December 31, they would be scheduled to receive an email on January 30.
This latter example illustrates why using the back-populate feature with flows that span several months is so powerful. You don't need to wait a long time for the flow to start sending. In fact, you can create your flow and start sending emails the same day or the next day based on historical behaviors.
If you have to, it safe to back-populate a flow more than once -- nobody will be scheduled to receive the same email more than once.
It is common to back-populate a flow more than once if you add another email to a flow and want to ensure everyone already queued up is scheduled to receive your newly added email.