How to detect duplicates when importing?

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1

Hello,

how to detect duplicates when importing ?

thanks

2

This is the default module, without any customizations?
https://support.sugarcrm.com/Documentation/Sugar_Developer/Sugar_Developer_Guide_11.0/Data_Framework/Vardefs/Specifying_Custom_Indexes_for_Import_Duplicate_Checking/index.html

or you have to check this extension: Duplicate detector