I have a large file of 5,000 emails that I need to update and remove them from salesforce.com using the dataloader, however the Contact ID Field was deleted from the spreadsheet. I have the original file of 11,000 emails with contact IDs and the file of the 5,000 emails which are from the original 11,000 file. Is there a way to retrieve or look up contact IDs based on data from an excel file?

I have a large file of 5,000 emails that I need to update and remove them from salesforce.com using the dataloader, however the Contact ID Field was deleted from the spreadsheet. I have the original file of 11,000 emails with contact IDs and the file of the 5,000 emails which are from the original 11,000 file. Is there a way to retrieve or look up contact IDs based on data from an excel file?