Send email to a friend is not working

Check you've got postfix installed and make sure you've configured it. Otherwise check IPTables to ensure you've not got an outbound drop rule that's not allowing if out.

Check IPTables with iptables -L if that has no rules then please share with me your post fix configuration.

Also check the service via service postfix status

Try this,

Got to System Transaction mail and load Send Product to Friend and check it loaded or not

then go to System -> Configuration -> Catalog -> Email to a Friend and check below configuration is fine or not

then check if not working share me your error.log