I'm using the Public frontend premium plugin with uddeIM.
All works correctly. But, since the unregistered user is submitting their name and email address I believe that for legal reasons (privacy) it is necessary to add a checkbox whereby they have to accept the site terms and conditions when they submit a message (the same as when a new user registers with the site).
On the other hand whenever a user emails another user he gives his email address away, so does the user when he uses the public frontend instead. So I doubt that you have a privacy issue when a user submits his email address for that reason. You surely may have an issue when you are collecting these addresses and sell them or use them for ads etc.
uddeIM & uddePF Development
CB Language Workgroup
CB 3rd Party Developer
I don't sell the addresses or create a mailing list but I am collecting personal data because the users email address is saved in my database (in the recipient's inbox). So as far as I understand it I am obliged to at the very least inform the sender of this either by a link to the T&C or some text at the bottom of the form.