just yesterday i come across the fact that google mail/ gmail ignores the dot symbol in your username. eg. if you have googlemail or gmail accoung and your username happens to be something like my.username@gmail.com then its equivalent to all below:

1. myuser.name@gmail.com

2. my.user.name@gmail.com.

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.

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n. m.y.u.s.e.r.n.a.m.e@gmail.com

benefit of it is you can have multiple sign ups in social networking sites like twitter with single account as for twitter will treat all of above to be different person or email-address, and all of above account email will end up in your mailbox my.username@gmail.com.

Try it yourself and enjoy.