Mostly, Magento Email To A Friend or Send To A Friend on the product details page. user does not send an email to you’re friend until . he/she does not logged in.
If you want to send an email to you’re friend without loggin. Please follow below step.
Login Backend >> System > Configuration > Email to a Friend
set Allow for Guests = Yes
Now Refresh cache Go To >> System >> Cache Management and than see you’re product page.