Incoming Mail Routing

Disk Layout

Message Store

Data Store

Index Store

Backup

Redo Log

Log

The MTA server receives mail via SMTP and routes each mail message to the appropriate Zimbra mailbox server using LMTP. As each mail message arrives, the Zimbra server schedules a thread to have Lucene index it.

Disk Layout

The mailbox server includes the following volumes:

•	Message Store. Mail message files are in opt/zimbra/store

•	Data Store. The MySQL database files are in opt/zimbra/db

•	Index Store. Index files are in opt/zimbra/index

•	Backup Area. Full and incremental backups are in opt/zimbra/backup

•	Log files. Each component in the Zimbra Collaboration Suite has log files. Local logs are in /opt/zimbra/log

Note: The system logs, the redo logs, and the backup disk should be on separate disks to minimize the possibility of unrecoverable data loss in the event that one of those disks fails.

Message Store

The Zimbra Message Store is where all email messages reside, including the message body and any file attachments. Messages are stored in MIME format.

The Message Store is located on each Zimbra server under
/opt/zimbra/store. Each mailbox has a dedicated directory named after its internal Zimbra mailbox ID.

Note: Mailbox IDs are unique per server, not system-wide.

Single-Copy Message Storage

Single copy storage allows messages with multiple recipients to be stored only once in the file system. On UNIX systems, the mailbox directory for each user contains a hard link to the actual file.

Hierarchical Storage Management

Hierarchical Storage Management (HSM) allows you to configure storage volumes for older messages. To manage your email storage resources, you can implement a different HSM policy for each message server. Messages and attachments are moved from a primary volume to the current secondary volume based on the age of the message. The messages are still accessible. See Global HSM.

Data Store

The Zimbra Data Store is a MySQL database that contains all the metadata regarding the messages including tags, conversations, and pointers to where the messages are stored in the file system.

Each account (mailbox) resides only on one server. Each Zimbra server has its own stand alone data store containing data for the mailboxes on that server.

The Data Store contains:

•	Mailbox-account mapping. The primary identifier within the Zimbra database is the mailbox ID, rather than a user name or account name. The mailbox ID is only unique within a single mailbox server. The Data Store maps the Zimbra mailbox IDs to the users’ OpenLDAP accounts.

•	Each user’s set of tag definitions, folders, and contacts, calendar appointments, tasks notebooks, and filter rules.

•	Information about each mail message, including whether it is read or unread, and which tags are associated.

Index Store

The index and search technology is provided through Apache Lucene. Each message is automatically indexed as it enters the system. Each mailbox has an index file associated with it.

The tokenizing and indexing process is not configurable by administrators or users.

Figure 3: Message tokenization

The process is as follows:

1.	The Zimbra MTA routes the incoming email to the Zimbra mailbox server that contains the account’s mailbox.

2.	The mailbox server parses the message, including the header, the body, and all readable file attachments such as PDF files or Microsoft Word documents, in order to tokenize the words.

3.	The mailbox server passes the tokenized information to Lucene to create the index files.

Note: Tokenization is the method for indexing by each word. Certain common patterns, such as phone numbers, email addresses, and domain names are tokenized as shown in Figure 3.

Backup

Zimbra includes a configurable backup manager that resides on every Zimbra server and performs both backup and restore functions. You do not have to stop the Zimbra server in order to run the backup process. The backup manager can be used to restore a single user, rather than having to restore the entire system in the event that one user’s mailbox becomes corrupted. See Backup and Restore.

Redo Log

Each Zimbra mailbox server generates redo logs that contain current and archived transactions processed by the message store server since the last incremental backup.

When the server is restored, after the backed up files are fully restored, any redo logs in the archive and the current redo log in use are replayed to bring the system to the point before the failure.

When the current redo log file size reaches 100MB, the current redo log rolls over to an archive directory. At that point, the server starts a new redo log. All uncommitted transactions from the previous redo log are preserved. In the case of a crash, when the server restarts, the current redo log are read to re-apply any uncommitted transactions.

When an incremental backup is run, the redo logs are moved from the archive to the backup directory.

Log

A Zimbra deployment consists of various third-party components with one or more Zimbra mailbox servers. Each of the components may generate its own logging output.

Selected Zimbra log messages generate SNMP traps, which you can capture using any SNMP monitoring software. See Monitoring Zimbra Servers.