ZCS Administrator's Guide, Open Source Edition, 6.0.8
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Product Overview : System Architecture

System Architecture
Figure 1 shows the Zimbra Collaboration Suite architectural design, including the open-source software bundled with the Suite and other recommended third-party applications.
Figure 1: ZCS Collaboration Suite System Architecture
 
 
Zimbra Packages
The Zimbra Collaboration Suite includes the following application packages.
Zimbra Core
The Zimbra Core package includes the libraries, utilities, monitoring tools, and basic configuration files.
Zimbra LDAP
The Zimbra Collaboration Suite uses the OpenLDAP software, an open source LDAP directory server. User authentication is provided through OpenLDAP. Each account on the Zimbra server has an unique mailbox ID that is the primary point of reference to identify the account.
The OpenLDAP schema has been customized for the Zimbra Collaboration Suite.
Zimbra MTA (mail routing server)
Postfix is the open source mail transfer agent (MTA) that receives email via SMTP and routes each message to the appropriate Zimbra mailbox server using Local Mail Transfer Protocol (LMTP). The Zimbra MTA also includes the anti-virus and anti-spam components.
Zimbra Store (Zimbra server)
The Zimbra store package installs the components for the mailbox server, including Jetty, which is the servlet container the Zimbra software runs within. Within ZCS, this servlet container is called mailboxd.
Each account is configured on one mailbox server, and this account is associated with a mailbox that contains all the mail messages and file attachments for that mail account.
The mailbox server includes the following components:
Each Zimbra server has its own standalone data store, message store and store for the mailboxes on that server.
As each email arrives, the Zimbra server schedules a thread to have the message indexed (Index store).
 
Data store.
The data store is a MySQL database where internal mailbox IDs are linked with user accounts. The data store maps the mailbox IDs to users’ OpenLDAP accounts. This database contains each user’s set of tag definitions, folders, calendar schedules, and contacts, as well as the status of each mail message - read, unread, tags associated to message, and folder the message resides in.
Message store.
The message store is where all email messages and file attachments reside. Messages are stored in MIME format. A message that is sent to multiple recipients who have accounts on one mailbox server are stored only once in the file system.
Index store.
Index and search technology is provided through Lucene. Index files are maintained for each mailbox.
Zimbra-SNMP
Installing the Zimbra-SNMP package is optional. If you choose to install Zimbra-SNMP for monitoring, the package should be run on every server (Zimbra server, Zimbra LDAP, Zimbra MTA) that is part of the Zimbra configuration. Zimbra uses swatch to watch the syslog output to generate SNMP traps.
Zimbra Logger
Installing the Zimbra Logger package is optional and is installed on one mailbox server. The Zimbra logger installs tools for syslog aggregation, reporting. If you do not install Logger, the server statistics section of the administration console will not display.
Zimbra Spell
Installing the Zimbra Spell package is optional. Aspell is the open source spell checker used on the Zimbra Web Client. When Zimbra-Spell is installed, the Zimbra-apache package is also installed.
Zimbra Proxy
Installing the Zimbra Proxy is optional. Use of an IMAP/POP proxy server allows mail retrieval for a domain to be split across multiple Zimbra servers on a per user basis.
Note: The Zimbra Proxy package can be installed with the Zimbra LDAP, the Zimbra MTA, the Zimbra Mailbox server, or on its own server.
Zimbra Memcached
Memcached is a separate package from zimbra-proxy and is automatically selected when the zimbra-proxy package is installed. One server must run zimbra-memcached when the proxy is in use. All installed zimbra-proxies can use a single memcached server.
 
Zimbra System Directory Tree
Table 1 lists the main directories created by the Zimbra installation packages.
The directories not listed in this table are libraries used for building the core Zimbra software
Note: The directory organization is the same for any server in the Zimbra Collaboration Suite, installing under /opt/Zimbra.
Table 1 Directory Structure for Zimbra Components
 
/opt/Zimbra/
Zimbra application files, including the utilities described in Appendix A, Command -Line Utilities
mailboxd application server instance. In this directory, the webapps/Zimbra/skins directory includes the Zimbra UI theme files.

Product Overview : System Architecture

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ZCS Administrator's Guide, Open Source Edition, 6.0.8
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