I have a spreadsheet in which I suspect there are duplicate email IDs. Does Zoho CRM automatically prevent import of these duplicates?
No. Zoho CRM does not prevent duplicates during import if they are within your import spreadsheet.
However, Zoho CRM provides duplicate check during import on email addresses with records that already exist in the CRM database. When this feature is enabled, the CRM matches the email addresses in your spreadsheet with those in the database and throws out an alert if it finds duplicates. On the other hand, if you are making an import for the first time and there are duplicates within your spreadsheet, enabling this feature will not remove those duplicates. The only way to prevent this is to make sure your import sheet is free from duplicates.
To enable the feature
Click Setup > Customization > Modules and Fields.
In the Modules page, select the Leads/Contacts module. You need to enable it separately for the Leads and Contacts modules.
Select the Do not allow duplicates values for the Email field. This option is available in the Module layout for all unique fields such as Email, Phone Number, Mobile Number, Company etc. When you enable this option in the module layout, you can select the module for which you want the duplicate check to work while you're importing.
Click Save. You can disable this feature by clearing the Do not allow duplicates in Email field check box. Alternatively, you can merge duplicates after you import your leads. Zoho CRM offers two ways by which you can merge duplicate records.
Find and Merge Duplicates
Deduplicate tool (available only in the Professional, Enterprise editions and above).