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.