I want to push my yahoo mail to my gmail inbox automatically.
You can set your g-mail up to pull from your yahoo. I'm not sure if you can set an auto forward via yahoo, but any of this is things you'll need to do via computer or safari, it won't work via the mail app.
From the Mail app, you can't. You will need to log into your yahoo account via a browser and set up autoforwarding there.
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