Import People via CSV
This page takes you through the process of importing people by CSV. When you import a CSV, you can determine whether to add new people, update existing people, or both.
CSV Requirements
You can upload a CSV directly into Customer. io, or link us to a Google Sheet. Take a look at an example CSV.
Each row in your CSV represents a person you want to add to your workspace, and each column represents an attribute that you want to assign to that person.
Attributes are case sensitive
Your file must:
- be in CSV format OR a Google Sheet
- not exceed 100MB in size
- not contain more than 100 columns
- contain a column that maps to either the
id
oremail
attribute in Customer.io:- Adding people to email-based workspaces: your list must have a column that maps to
email
. - Adding people to
id
-based workspaces: your list must have a column that maps toid
.
- Adding people to email-based workspaces: your list must have a column that maps to
- Google Sheets be shared with cio_share@customer.io. (You can also make your sheet public, but we strongly discourage the use of public sheets for security reasons).
Upload a CSV to Customer.io
Before you import people, make sure that your CSV file is ready to import. It must contain a column that maps to either id
or email
attributes in Customer.io. If importing a Google sheet, your sheet must be shared with cio_share@customer.io
.


-
Go to either:
- Imports > Import People
- People > Add People > Import a CSV.
-
Select the file you want to import.
-
Set a Name and Description for your import, helping you identify your CSV on the Imports page.
-
Determine how to handle your import and then click Next:
- Add new people or not.
- Update existing people. If you update existing people, determine whether to update people by
id
oremail
. - Determine how to handle empty values—ignore them or nullify existing attribute values.
-
Map fields from your CSV to attributes in Customer.io and click Next. You must map
id
oremail
attributes to a column if your sheet did not include columns labeledid
oremail
; all other columns are optional.Creating new attributes
If you import a column, but you don’t map it to an existing attribute, we create a new attribute using the column title. -
Review your import for errors and warnings. Click Preview Import to download a CSV file that reflects your final import, including all data mappings, skiped attributes, etc. Make sure that your import is correct. You cannot stop the import process after you click Import.
-
(Optional) Select the boxes below the Review your data section to add imported people to a new or existing segment.
Imports process in sequence
Customer.io processes imports row-by-row. Segment-triggered campaigns may fire as we create new people or change attributes, so review your import carefully. -
Click Complete import. It takes approximately one minute per 20-30 thousand rows to import your file. You can navigate away from the page. We will send you an email when your import is complete.
Go to Data & Activity > Imports to revisit this import or see your previous imports.
Mapping CSV headers to attributes
When you import a CSV, you match the headers in your CSV to attributes for people in Customer.io. If your column names match attributes in Customer.io, we try to map them automatically. Otherwise, you can re-map columns in your attribute to existing attributes or create new attributes.
We sample the first three rows of your data for each column, helping you understand the data that you’re mapping to each attribute. Use Import as: to select the attribute that you want to map a column to. If you do not want to import the values in a column, select Skip.


Customer.io has four reserved attributes: id
, email
, created_at
, and unsubscribed
. If you want to import a column representing an ID, but you don’t want to map that to the reserved Customer.io id
attribute, you can change the column name and import it as a different attribute.
Mapping warnings
Reserved Attributes
When mapping data to reserved attributes, make sure you use the correct data format, described below:
Attribute | Purpose | Required | Data Format |
---|---|---|---|
id | This is the unique identifier for people. If the id does not yet exist, we create a new person. You cannot include id when adding people to email-based workspaces. |
When importing by id |
Our default id limit is set to 150 characters. All valid utf characters are allowed. |
A person’s email address and the unique key by which you identify people in email-based workspaces. The TO line of your email templates is prefilled with this attribute. | When importing by email | We support valid RFC 5322 email addresses. | |
created_at | Recommended. Holds the date when a profile was created. This value lets you to take advantage of timestamp operators in segments and helps you determine the age of a person’s profile. | Optional | We support: - unix epoch - unix epoch ms - ISO 8601 |
unsubscribed | Determines whether a person is subscribed or unsubscribed from your campaigns and newsletters. (reference) | Optional | We support any case of true (i.e. TRUE , true , tRUe , etc.) or ‘1’ to represent unsubscribed. Any other value is considered “false”, or subscribed. |
mobile_ad_id | Used to record either Apple’s Advertising Identifier (IDFA) or Android’s Advertising ID (AAID). This id can improve match accuracy in Google or Facebook Ads when using Ad Audiences. | Optional | Apple’s Advertising Identifier (IDFA) or Android’s Advertising ID (AAID) |
email_sha256 | To keep your data secure, you can hash your customer email using the SHA256 algorithm before sending it to your account. This field is only used in Ad Audiences and cannot be used to send messages. | Optional | Valid encoded sha256 |
mobile_ad_id_sha256 | To keep your data secure, you can hash the mobile_ad_id using the SHA256 algorithm before sending it to your account. This field is only used in Ad Audiences. | Optional | Valid encoded sha256 |
Importing by id
When you import users by id, your CSV file must contain a column that maps to id
. If your id
column is not named id
, you will map the column to id
.
Profile IDs are unique and cannot be changed. In most workspaces, where you assign id
as the unique people-identifier, Customer.io de-duplicates profiles on id
, but the same email address can be used across multiple IDs.
If you assign the same email address to multiple IDs, you may send people duplicate messages. Before you import people or create new profiles, check with your technical team to understand how you assign and organize profiles to make sure that you don’t inadvertantly add duplicates to your workspace.
Importing by email
When you add people to an email-based workspace, or update people by email address, your CSV file must contain a column that maps to the email
attribute.
If your email
column is not named email
, you will map the column to email
.
When importing people to an email-based workspace, your CSV file cannot contain an id
column. In email-based workspaces, we auto-generate ids for people.
Updating emails in email-based workspaces
id
.Reviewing import errors and warnings
On the Review step when you import a CSV file, we validate your import, returning errors and warnings for rows in your CSV file. Rows with errors will not be imported.
Depending on the size of your CSV file, it may take a moment for us to validate your import.


If there are no errors or warnings, you can continue importing your file as normal. If not, you may want to correct issues in your your CSV file to make sure that you import everybody in your CSV.
- Errors: issues that prevent us from importing a row. Example: *The row is missing a value in the
id
column._ - Warnings: issues that do not prevent us from importing a row, but you may want to note to make sure that your data is well formed. You probably don’t need to fix issues resulting in warnings. Example: The same email address is used for multiple ids and will create multiple people.
In Import Details, you can click ERRORS or WARNINGS to download a CSV file containing either errors or warnings. Each file contains the rows from your original CSV file that resulted in errors or warnings respectively, including 2 new columns:
- _row: contains the row number from your original file that contained an error or warning.
- _errors or _warnings: lists errors/warnings for a row.
Re-import your error CSV
Exporting files from an import
Files supplied or generated during your import expire and will no longer be available for download after 30 days.