For this purpose you can use GAWK. It's an open-source application bundled with GnuWin32 (but it can be downloaded as a single package) which is used for procedures like these. Please download and install the application then start a Command Prompt. If you use Windows Vista, 7 or 8 you will need to open a Command Prompt with elevated access.
Move the file with your content in a place that is easy to access like: C:\dupe or D:\dupe for easy handling then use the following command: awk "!x[$0]++" file.csv > results-new.cvs. The file without duplicated e-mails will be saved to results-new.csv. The file.csv needs to have the path to the original file.