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 that 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 to 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
When you back-populate a flow that is triggered by being added to a list and segment, you will have two options: back-populate recipients relative to when they were added to the list/segment, or back-populate recipients relative to when you click back-populate.
If you choose to back-populate your flow relative to when customers were added to the list/segment, people will only receive the emails if they fall within the time parameters of the flow.
For example, let's say you have one email in the flow that goes out immediately, and another that goes out 2 days later. If you back-populate this flow, anyone who was added to the list less than 2 days ago will receive the second email, but not the first (since they would have received it immediately).
If you choose to back-populate your flow relative to when you click Back-Populate, each person will be queued as if they had been added to the list or segment immediately.
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.
If you back-populate a list-based flow that has recipients in the Needs Review tab, once you approve the email to be sent, it will go out immediately.
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.
It is common to back-populate a flow more than once if you add another email to a flow and want to ensure that everyone already queued up is scheduled to receive the new email. No one will be scheduled to receive the same email more than once.
If you back-populate an event-based flow that has recipients in the Needs Review tab, recipients will get the email depending on when they triggered the flow. If someone was scheduled to receive the email before you approve the email, it will be sent immediately. If someone is scheduled to receive the email after you approve the email, they will receive it when they normally would.
So, for example, let's say you back-populate a flow that is supposed to start sending after 2 hours and there are recipients in the Needs Review tab. Once you approve these emails, anyone who triggered the flow less than 2 hrs ago will receive the email 2 hrs after they triggered the flow, and anyone who triggered the flow more than 2 hrs ago will receive the email immediately.