Send e-mail to "uid"

I've got a node type which are selling items, there are multiple authors on creation of these nodes and I want to be able to get Anonymous users react to those items by sending a e-mail to the author of the selling item. I could make a post form which sends over the "user_load($node->uid)->mail" variable, but as I don't want to expose the e-mail adresses of the authors, I would like to send over the uid of the authors and then make the webform to select the e-mail address by itself.

Is this by any means possible? I'm familliar with PHP and some basic experience with adjusting modules and template.php files, so any push in the right direction would be greatly appreciated.

I thank you in advance.