The central message store in a legacy Microsoft Mail system.
The postoffice consists of a series of message storage directories on the Microsoft Mail file server. The postoffice stores information such as user ID, password, user preferences, message folders, mail messages, and attachments.
The postoffice is a passive file system; no active software runs on it. The International Telecommunication Union (ITU) refers to this component of a mail system as the «message store».