Hi Nazima,
To explain this better let us consider a list with the following structure and items:
Model ID | Model Name |
1 | Model1 |
2 | Model2 |
3 | Model3 |
If you drag in the "Model ID" column into this field the InstanceData of the Activity Destination will be the ID of the model, in other words 1,2,3. If you select the "Model Name" column the InstanceData field will be set to "Model1","Model2","Model3".
It depends what you need to do in your Email event, but I think the ID column will be better for most purposes. You can then take the InstaceData property and use the value in it as an input parameter to call a SmartObject Load method. Load methods normally take the ID property as input so by passing in the ID value you should get unique data in your Email event for the current instance.
I hope this made sense. Let me know if something was unclear.