https://gmail.google.com/support/bi...r=7403&topic=-1

How do I invite others to join Gmail?

Answer

Because we're currently only offering Gmail as part of a preview release and limited test,
we don't have details on when Gmail will be made more widely available.

As we make way for more accounts, we may periodically allow you to invite others to join Gmail.
When we do so, you will see an invitation link in your inbox.

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