> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mention-me.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Exclude Existing Customers
> How to upload a list of existing customers to prevent them from receiving new customer referral rewards.
## Why exclude existing customers?
When launching your referral programme, you may want to prevent existing customers from being treated as new customers and receiving referral rewards. Upload a list of customer emails to automatically exclude them from new customer rewards. They can still enrol as referrers and refer friends.
We generally recommend using data covering the last 12 months of trading activity. The data requirements are outlined in the Data Processing Agreement (DPA) in your contract.
## What does this do?
After uploading your customer data, only new customers who have not yet made a purchase will be eligible for referral rewards. Existing customers attempting to claim new customer discounts will see a message indicating they are not eligible.
## How to do it
### 1. Export data from your site or CRM
Create or export a CSV file containing email addresses for the period you choose (usually 12 months). The file should have one column with a header row.
| Field | Type | Example |
| -------------- | ----------------------------------------------------------------------------------- | ----------------------------------- |
| Customer Email | Email or [hashed email](/knowledge/security/data-management/hash-historical-emails) | [name@xyz.com](mailto:name@xyz.com) |
### 2. Upload your data to Mention Me
Using the [historical customer uploader](https://mention-me.com/merchant/~/upload/customers):
1. Select the file you exported
2. Map the `Email` field to the email column using the mapper
3. Verify the sample columns match the expected data
4. Click **Upload**