ezsystems/ezsurvey — pull request #7 by peterkeung (2012-02-29 23:26:47+00:00)
Title: Support an option to make EmailEntry responses unique

Survey responses for contests, registrations, or similar could have a requirement that you only want one entry per e-mail address. This adds a checkbox to specify that an e-mail field answer must be unique across all answers to the survey.