This article outlines the process of contacting an author of a Discussions post by email. Typically, the email option is only available for instructors or site owners.
Note: This email reply option sends a message to the author's external email address. It does not use the internal Messages tool to send the message.
Select Discussions.

Select Discussions from the site's Tool Menu.
Select a forum.

Select the title of a forum.
Select the Topic within the Forum.

This is an example of a Topic. Select the Topic to view conversations posted to that topic.
Select the conversation.

Select a conversation (a topic thread) by selecting its title.
Select Email.

Select Email below the author name in order to email the post author. Selecting Email will open a draft message to the author in your computer's default mail client (e.g., Outlook).