Hello @mattelustra ,

Thanks for sharing to the Community.

That would depend on if users did not exit the flow already. Flows work in real-time, so if you add another step to a flow, you do not need to back-populate if you only want recipients who are still in the flow (i.e., have not gone through the last step yet) and who haven’t passed the new step to go through it.
 
Here is more information on How Back-Populating Works in Klaviyo.

Hope that helped,

Alex

Thank you. So if a user had already reached the last email, I would need to back populate in order for them to receive a newly created email?

Thats correct @mattelustra 

@alex.hong  thanks for the explanation, very helpful!.

Additional question: if you back-populate to enter profiles again to receive an newly added e-mail (as described above), are existing e-mail that are already received automatically skipped, or do I need to change a setting for that?

Hi @Ruud - The Bulb Farmers ,

If you are afraid of back populating as it might include people that should not be included, I highly suggest you putting this flow as MANUAL MODE and back populate. When a message is in manual, it is active in your flow but no emails or SMS will send automatically at send time; you will need to review and send all scheduled messages manually. Here is a great article on this: https://help.klaviyo.com/hc/en-us/articles/115002779331-How-to-Manually-Send-Flow-Messages-to-Recipients 

You will need to back-populate to send a new added action (email) to those who have either exited the flow or continued past the point of the new message. If you added a new action at the end of the path that this profiles has already gone down, you can back-populate to queue this profile for the new message.
That said I would highly suggest putting the Flow in manual to back populate as mentioned before and make sure which profile will be added to each email with back population.

Once you've entered a list-based flow you cannot be re-queued for any flow message you have already received. That said if someone already entered the Flow and received the emails before this person will not be re-queued again for the same List based flow even if you back populate. 

When you schedule recipients based on when you back-populate, this treats recipients as if they just joined your list or segment. They’ll start at the very beginning of the flow and move through it one step at a time, like any other recipient. If you back-populate via this option, everyone who qualifies for the flow (except for those who have already entered the flow) will start at the trigger. Those who already went through the flow will not receive the same messages again, while everyone else will start at the beginning and move through it step-by-step.

oke thanks.