This plugin adds two links below each comment and each discussion: "Send PM" and "Reply". Send PM will redirect to /messages/add/username/discussionname which creates a new conversation with the author of the post as the recipient and the title of the discussion as the subject.
Both links can be deactivated individually by setting reply.SendPM or reply.Comment = false in the config.php.
Sources on GitHub
Fixed: Make js work with iframe of advanced editor
Fixed: Prevent wrong url when forum is in a subdirectory
ToDo: Set cursor at end of text in advanced editor
Don't show buttons for guests any more
Add css class to session users own discussions so that buttons can be hidden/styled the same way that they can be in comments.