Get users email id

Is there any way to get the user's email id from my app automatically.. instead of asking the user to register with his email id or something like that....

I want to know who all bought my app, and want their email-id's to send them more info via mail..

thanks in 开发者_开发知识库advance...

As a general rule of thumb, users should always be given the choice to "opt-in" and register that level of detail to receive additional information if they so desire. Harvesting the email address without them knowing about it would not be a good idea.

As I know, there is no such facility. You should provide users with a Register facility to be informed about the updates. I think people will willingly register as they are paying for the app.