What to take instead of the email API from users of Facebook?

Try openAPI and secure.sendNotification to send a notification to the user. However, I'm not sure that will work.

I would do the following:
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A key goal — feedback "already a user" of the service. You can track via that registered with the user and after some time or when performing a specific action to give him a "Like" button or subscribe to the feed. Then you will have it in news feed. His email is in this case not really needed.

1) at first login popup to display and to require email, first check whether you do not violate the terms of service. But it's impolite to your users.
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1a) when you first login display popup and offer the bonus, for example, the new aluminum armor, enter your email, first check whether you do not violate the terms of service. But it's annoying.
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1b) to give a bonus for likes of pages and adding a site (application) in the left menu. Do not forget to take away the bonus when unlike.But it's annoying.
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2) check the terms of service and if not prohibited, spamming the user notifications from apps. But it's annoying.
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3) check the terms of service and if not prohibited, to spam the user wall. But it's impolite to your users.

we take the interests of users

And how through the API you get them?

And from FB, you can email to take?

VKontakte now also email-s gives, so you can not reinvent the great)
Here more described: habrahabr.ru/post/168295/#comment_7568079

1) email to you, just scope during authorization add another email.
2) you can create advertising company to everyone who is authorized through your app, not free, but quite effectively.