I've installed the webform module in my drupal site and want to configure it so that the submission limitation is by email instead of cookies. I dont want users who have already submitted to submit twice if their email is in the system. Is there a way to do that? Would I Have to create a new module for this? If so, how do I communicate my new module with the webform module? Or would editing this webform module be the solution (which I dont think is a good idea in case I have to upgrade it and lose the changes I've done). Please help. Thanks.
You can use the webform validation to create a rule that compares the e-mailaddress with all e-mailaddresses in the table where the webform data is stored (you will have to look it up but I believe it is the email field in the webform_emails table).
Or you can create a custom module depending on webform_validation to compare data, there is a similar issue in the issues..