The Message Store

The Message Store is a dedicated data store for the delivery, retrieval, and manipulation of Internet mail messages. The Message Store works with the IMAP4 and POP3 client access servers to provide flexible and easy access to messaging. The Message Store also works through the HTTP server (mshttpd) to provide messaging capabilities to Communications Express in a web browser. In addition to this section, see Chapter 20, Managing the Message Store, in Sun Java System Messaging Server 6.3 Administration Guide for more information.

The Message Store is organized as a set of folders or user mailboxes. The folder or mailbox is a container for messages. Each user has an INBOX where new mail arrives. Each IMAP or Webmail user can also have one or more folders where mail can be stored. Folders can contain other folders arranged in a hierarchical tree. Mailboxes owned by an individual user are private folders. Private folders can be shared at the owner’s discretion with other users on the same Message Store. Messaging Server supports sharing folders across multiple stores by using the IMAP protocol.

There are two general areas in the Message Store, one for user files and another for system files. In the user area, the location of each user’s INBOX is determined by using a two-level hashing algorithm. Each user mailbox or folder is represented by another directory in its parent folder. Each message is stored as a file. When there are many messages in a folder, the system creates hash directories for that folder. Using hash directories eases the burden on the underlying file system when there are many messages in a folder. In addition to the messages themselves, the Message Store maintains an index and cache of message header information and other frequently used data to enable clients to rapidly retrieve mailbox information and do common searches without the need to access the individual message files.

A Message Store can contain many message store partitions for user files. A Message Store partition is contained by a file system volume. As the file system becomes full, you can create additional file system volumes and Message Store partitions on those file system volumes to store new users.

If the partition gets full, users on the partition will not be able to store additional messages. There are several ways to address the problem:

• Reduce the size of user mailboxes

• If you are using volume management software, add additional disks

• Create additional partitions and move mailboxes to the new partitions

For more information, see Chapter 20, Managing the Message Store, in Sun Java System Messaging Server 6.3 Administration Guide.

The Message Store maintains only one copy of each message per partition. This is sometimes referred to as a single-copy message store. When the Message Store receives a message addressed to multiple users or a group or distribution list, it adds a reference to the message in each user’s INBOX. Rather than saving a copy of the message in each user’s INBOX, Message Store avoids the storage of duplicate data. The individual message status flag (seen, read, answered, deleted, and so on) is maintained per folder for each user.

The system area contains information on the entire Message Store in a database format for faster access. The information in the system area can be reconstructed from the user area. Messaging Server contains a database snapshot function. When needed, you can quickly recover the database to a known state. Messaging Server also has fast recovery, so that in case of database corruption, you can shut down the Message Store and bring it back immediately without having to wait for a lengthy database reconstruction.

The Message Store supports per-user quotas. Enforcement of quota can be turned on or off. You can configure a user quota by using number of bytes or number of messages. You can also set a threshold so that if the quota reaches the threshold, a warning message can be sent to the user. When the user is over quota, new messages can be held up for retry during a grace period. After the grace period, messages sent to the over-quota user are returned to the sender with a non-delivery notification.

For special applications where quota is used, but messages must be delivered regardless of the quota status of the users, there is a guaranteed message delivery channel. This channel can be used to deliver all messages regardless of quota status. Utilities are available for reporting quota usage and for sending over quota warnings.