If you are exporting from the listview, the export file will contain every field from the database within the given module.
If you want to have control of which fields to be in the export file (and which to exclude), a good way is to create a Rows and columns Report and use it to export the Contacts without the email address field.
If it's just a question of creating an export without email address you can do that with Andre Serrazina 's suggestion.
But if you are trying to keep a user from downloading a list of your customers' email addresses and selling it, or taking it with them to the competition, then there is nothing you can do, even if you disable the export, keep in mind that whatever one can see in the front end one can access using an API call with the same credentials as the front-end application..
