[Plugin: Grunion Contact Form] Give users choice of email recipient

The website I’m making is for a printing company containing 3 major departments. I have included a drop-down menu for users to select the department they need to contact, but I don’t know how to make it send the email to the selected department. How can I do this?

Thanks,
Rebecca

http://wordpress.org/extend/plugins/grunion-contact-form/