This lesson covers two things: getting subscriber data into Bento safely, and running transformations across subscribers who are already there.
The import side is straightforward - Bento's import guide walks you through the CSV format and process step by step.
The backfill side is where people get into trouble.
When you have hundreds or thousands of existing subscribers and need to run some automation across all of them, doing it wrong can mean accidentally sending emails to people who shouldn't get them, or overwriting data you didn't mean to touch.
Here's how to handle both.
How To Import Data
Bento imports subscribers via CSV.
The import guide has the full step-by-step, sample CSV templates, and formatting examples.
Defer to that for full importing training, as that guide is very detailed and helpful.
My Personal "Backfill" / Bulk Operation Process
A "backfill" is when you need to run some transformation across a group of subscribers who are already in your Bento account.
Common scenarios:
- You imported a list from another ESP and need to set up their tags and fields to match your Bento schema
- You built a new automation flow and want existing subscribers to go through it
- You need to update a field value across everyone in a specific segment
It's conservative on purpose; the goal is to never accidentally blast emails to the wrong people or corrupt subscriber data.
Notes If You're Importing Subscribers First:
If you're bringing in new subscribers, import them clean.
No tag_as_event, no automation triggers. Just data.
(If the subscribers are already in Bento and you're running a transformation on existing people, skip this step.)
Then, tag the imported subscribers with a datestamped import tag.
Something like Import - 2026-07-14 - Migrated From Kit/ActiveCampaign/Whatever.
This gives you a clean handle to target exactly these subscribers in the next steps.
The date makes it easy to audit later.
Then spot-check a handful of subscriber profiles.
Verify the fields mapped correctly, the tags are there, and nothing looks off.
Fix issues now, before you trigger any automations.
So with all that said, here's my personal backfill / bulk operation process:
1 - Build the transformation flow
Create a Flow that does whatever you need: setting tags, updating fields, adding to sequences, sending emails, etc.
Use an event trigger with a name specific to this backfill, like backfill_ck_migration_july_2026.
If you need a refresher on building flows, see the Events & Flows Overview lesson.
2 - Test the flow on one subscriber
Manually fire the backfill event on a single test subscriber (that maps to YOUR email inbox) and verify the flow does what you expect.
Check their profile after: tags set correctly? Fields updated? Sequence membership right? Email sent (if applicable)?
We covered flow testing techniques in the Flow With Events, Tags, Fields, & Emails lesson.
3 - Deploy via bulk operation
Once you're confident the flow works correctly, use Bento's bulk operation feature to fire the event across your target segment:
- Select the segment you want to backfill (the people tagged with your import tag, or whatever segment defines your target group)
- Choose the backfill event you created as the flow trigger
- Run it
Bento processes the operation in the background.
Depending on the size of your segment, it can take anywhere from a few seconds to several minutes.
After it completes, spot-check a few subscriber profiles to confirm everything processed correctly.
You can also add a tag via that same bulk operation, e.g. Main Kit Import - Backfill Step 1 Done, to keep track of who you've run the backfill on.
Backfilling Sequences
One specific scenario worth calling out: if you add new emails to a sequence that some subscribers have already completed, those subscribers won't receive the new emails automatically, since they already left the sequence upon completing it.
Bento's backfill sequences guide covers how to handle this - including a clever prevention trick and a workflow-based fix for when it's already happened.
Worth reading before you run into it.
When To Move On
- You know where to find Bento's import guide and backfill sequences guide
- You understand the safe backfill process: import clean, tag, review, build flow, test, deploy via bulk operation