The MessageStore stores a copy of each message in each folder to which it is delivered.¹

Delivery can be directed to a user's INBOX or to any folder in the MessageStore if the folder's IMAP ACL permits posting. A message directed to

user+folder@host

will be filed into the specified folder named folder if the ACL permits; otherwise, it will be delivered to the user's INBOX.

A reserved name is used to deliver to public folders: by default the name post is used. A message directed to

post+folder@host

will be delivered to the public folder named folder if public posting is enabled; otherwise, the message will be returned to its originator as undeliverable.

A user's folders and messages are stored in a subdirectory of the directory containing the user's profile file as described in Section 1.3.9. Public folders are stored in a different directory tree. On UNIX systems, public folders are kept in the directory tree specified by the PMDF_MSGSTORE_MESSAGES option in the PMDF tailor file; on NT systems by the PMDF_MSGSTORE_MESSAGES registry entry; and, on OpenVMS systems in the PMDF_MSGSTORE_MESSAGES: directory tree as specified by the system-wide logical, PMDF_MSGSTORE_MESSAGES.

The IMAP protocol is used to manipulate folders and messages in the MessageStore. A number of IMAP clients provide rich management facilities including ACL and QUOTA support. User management is available through a command line interface, a web-based interface, and a subset of the popstore API as described in Section 2.6.