free email accounts gmail

question on free email accts wtih gmail or yahoo?

hi
why do gmail and yahoo provides free emai accounts to public
what do they gain by doing this..
because, i can undetsand it costs them a lot in maintaing servers,space, maintenance etc etc
but then why?
even if they charge few dollars per person,they should be making millions
why not they do…what is the business tactic here..

Duplicate question.

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