Automatic Customer Merging: How AutoLetter Detects Duplicates
3 min readLast updated: February 20, 2026Customers & Contacts
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When you connect multiple data sources with AutoLetter -- e.g., Shopify and Billbee or additional CSV imports -- it can happen that the same customer exists in multiple sources. AutoLetter automatically detects these duplicates and merges them into a single customer profile. This way, you avoid duplicate letters and maintain a clean customer overview.
AutoLetter checks each new customer record against existing customers. Four identification keys are used in a fixed priority order:
The most important match is by email address. Before comparison, the address is normalized: leading and trailing spaces are removed, and the entire address is converted to lowercase. This ensures that "Max@Example.com" and "max@example.com" are recognized as identical.
If two records have the same normalized email address, they are automatically merged.
If no matching email is found, AutoLetter checks the customer number. If your shop system or CSV import includes a unique customer number that already exists in an existing record, the entries are merged.
If there is neither a matching email nor a customer number, AutoLetter compares the full address. The following fields are checked together:
Only when all five fields match is a merge triggered. This minimizes the risk of false matches.
As a last resort, the internal system ID is checked. This fallback mainly applies to repeated imports from the same source, to recognize already known records.
When AutoLetter identifies two records as identical, they are merged into a single profile according to the following rules:
The name is taken from the first record that contains a complete name (first and last name). A record with only a first name is overwritten by a record with a full name.
Fields such as company, country, and city are filled from all available records. If a field is empty in the primary record, it is supplemented from another record. This creates the most complete customer profile possible.
All orders from all sources are displayed in the merged profile. Statistics (LTV, average order value, order count) are calculated across all orders.
Abandoned checkouts are not included in the calculation of statistics. Only actually completed orders count toward LTV and order count.
A customer is considered a repeat buyer as soon as they have more than one completed order -- even if these orders come from different sources. The merging ensures that a customer who placed one order in Shopify and another via Billbee is correctly counted as a repeat buyer.
After merging, the customer profile shows all sources as badges. This way, you can see at a glance that this customer was captured in both your Shopify store and via a CSV import, for example.
A customer places an order in your Shopify store with the email "anna@example.com". Later, you import a CSV file containing the same customer with "Anna@Example.com". AutoLetter normalizes both addresses to "anna@example.com", detects the match, and merges the records. In the customer profile, you then see both sources (Shopify + CSV) and all orders from both systems.
Automatic merging cannot be undone. If you discover that two different customers were incorrectly merged, please contact support.