I can't send the product recommend form if I'm not logged in.
I checked the shopFunctionsF::sendVmMail() function and $replyTo and $replyToName arrays are empty in here: $mailer->addReplyTo($replyTo, $replyToName);
I put a quick fix so if the replyto is empty I write the recipient into it but there should be some check for that :)
http://forum.virtuemart.net/index.php?topic=79800.0
If Joomla 3.5.1, update VirtueMart to 3.0.16.
You're right, I forgot the versions.
It's already Joomla 3.5.1 + VM 3.0.16
VM Configuration/Shopfront/Recommend a product, ask questions - "Allow non logged-in to send a recommendation or ask a question" set to YES.