Zimbra Mailbox Server

The Zimbra mailbox server is a dedicated server that manages all of the mailbox contents, including messages, contacts, calendar, Documents notebooks, and attachments. Messages are received from the Zimbra MTA server and then passed through any filters that have been created. Messages are then indexed and deposited into the correct mailbox.

Each Zimbra mailbox server in the system can see only its own storage volumes. Zimbra mailbox servers cannot see, read, or write to another Zimbra server.

In a ZCS single server environment, all services are on one server, and during installation the computer is configured to partition the disk to accommodate each of the services.

In a ZCS multi-server environment, the LDAP and MTA services can be installed on separate servers. See the Multi-Server Installation Guide.

Incoming Mail Routing

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

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

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.

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.

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.