Looking for E-Mail generator program

Hello, can anyone recommend a good program that will generate all possible combinations for an email address and check it against the server. For example check every possible email a-z for @gmail.com and check it to see if it's valid.

P.S. I'm not using this program for spam or anything like that. I need it for my own testing.

 

I think there is one, you just have to google for it. I think it was a Gmail generator account.