simple it will take a gmail like this.
agsfsgfakgfksgfaksgfkdafsdk@gmail.com
and give you all of the variations of it like this
a.gsfsgfakgfksgfaksgfkdafsdk@gmail.com
a.g.sfsgfakgfksgfaksgfkdafsdk@gmail.com
ag.sfsgfakgfksgfaksgfkdafsdk@gmail.com
ag.sfsgfak.gfks.gfaksgfkdafsdk@gmail.com
you get it?