Manitou-Mail is divived into three subsystems:
1) a PostgreSQL database that stores the messages contents and associated data.
2) a graphical user interface, responsible for the user interaction with the mail. It is a SQL client application that deals with mail messages and associated information in the database, and that doesn't store anything locally, nor talks directly to pop3, imap or smtp servers.
3) a server-side program that actually sends and receives messages, and carries out all the automated processing such as decoding, filtering and preprocessing.
This section of the documentation describes the graphical user interface.