The General settings provides a number of options to help in the functionality of the Private Messages plugin. Among these include:
Message Dashboard Page: This section enables you to specify the private messages dashboard page as outlined here.
Compose from Dashboard: Adds a link “New Message” to the message dashboard, of which once clicked, enables users to send messages from the message dashboard
Enable Message Attachments: Provides users with an option to incorporate attachments within their messages
Attachment max file size: This option enables you to define the maximum file size of attachments when sending messages.