Folder HelpDesk Exchange issue

Permission: “you don’t have permission to send a message to this recipient”

This is an Exchange issue. 

You and user helpdesk staffs should have ‘Send on behalf of’ rights over the support e-mail account that you have specified in the Folder HelpDesk Settings (Other settings tab > ‘Send e-mail from’ field). 

Your network administrator should be able to fix that in Active Directory.