We do not have a direct support for this. However, you can achieve your requirement by following the below kind of steps.
1. Create a new Drop down field to your form called (say Send Email) with the options Yes and No.
2. Navigate to the On Add ->On Load section of the form script and set up the value to it as “Yes” and hide the field.
The sample script can be,
input.send_Email = "Yes";
3. Then navigate to the On Add ->On Success section of the form and add a logic before the send email task as,
if (input.send_Email == "Yes")
To : zoho.adminuserid
From : zoho.adminuserid
Subject : "Your Subject"
Message : "<br />" + input.formdata
4. While importing data, you need not include the drop down field (send Email) in the XLS file. If you include you can use the value to it as “No”.
The above steps will assign the value to the send Email field as “Yes” only when the records are added via the Form.