We run an email groups service, like Google Groups. Groups can set the default to where replies to messages are sent to - either to the original sender or to the group. For a group that is set up so that the default is for replies to go directly to the sender, replying to a message on the web looks like this:
We prepend the word 'Private:' to the subject, and the button on the bottom left is labeled Reply to Sender.
If the person wishes to reply to the group instead, they click the 'Group Reply' button on the right. It looks like this then:
We remove the 'Private:' from the subject line, and change the Reply to Sender button to Reply to Group.
This set of interactions is confusing for some people. How can we make this functionality easier to use?
Edit: Additional Information
For completeness, here is the interaction when the group is set to Reply To Group by default:
And to make it a private reply, click the Private button on the right: