ZCS Administrator's Guide, Network Edition 5.0 (Rev 5.0.19 September 2009)
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Product Overview

Product Overview
This chapter describes the Zimbra application architecture, integration points, and information flow.
The Zimbra Collaboration Suite is designed to provide an end-to-end mail solution that is scalable and highly reliable. The messaging architecture is built with well-known open-system technology and standards and is composed of a mail server application and a client interface.
The architecture includes the following core advantages:
Open source integrations. Linux®, Jetty, Postfix, MySQL®, OpenLDAP®.
Uses industry standard open protocols. SMTP, LMTP, SOAP, XML, IMAP, POP.
Modern technology design. Java, JavaScript thin client, DHTML.
Horizontal scalability. Because each mailbox server includes its own data store, message store, and set mailbox accounts, you don’t change anything on existing servers in order to scale the system. To scale for additional mail accounts, add more servers.
High availability support. For cluster integration to provide high availability, ZCS can integrate with either Red Hat® Enterprise Linux® Cluster Suite version 4, Update 5 or later or with Veritas™ Cluster Server by Symantec (VCS) version 5.0 with maintenance pack 1 or later.
Browser based client interface. Zimbra Web Client gives users easy access to all the ZCS features.
Core Functionality
The Zimbra Collaboration Suite is an innovative messaging and collaboration application that offers the following state-of-the-art messaging and collaboration solutions:
The core functionality within ZCS is as follows:
Administrators can easily manage domains, servers, and accounts from the browser based administration console.
Zimbra offers two browser based web clients, Advanced Zimbra Web Client that offers a state-of-the-art Ajax web client; and Standard Zimbra Web Client as an HTML client. Some of the features that can be found in the web client include:
Zimbra Components
Zimbra architecture includes open-source integrations using industry standard protocols. The third-party software listed below is bundled with Zimbra software and installed as part of the installation process. These components have been tested and configured to work with the software.
OpenLDAP software, an open source implementation of the Lightweight Directory Access Protocol (LDAP) that provides user authentication
Verity®, a third-party source that converts certain attachment file types to HTML
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: Zimbra 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 (convertd) extracts the text from the attachments to be indexed along with the mail body.
Attachments are converted to HTML when users click on the view as HTML link on the Zimbra Web Client.
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, and message tracing. If you do not install Logger, you cannot use the message trace feature. In addition, the server statistics are not captured, and 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 Archiving
The Zimbra Archiving and Discovery feature is an optional feature for Zimbra Network Edition. Archiving and Discovery offers the ability to store and search all messages that were delivered to or sent by Zimbra. This package includes the cross mailbox search function which can be used for both live and archive mailbox searches. Note: Using Archiving and Discovery can trigger additional mailbox license usage. To find out more about Zimbra Archiving and Discovery, contact Zimbra sales.
Backup Process Overview
Zimbra includes a configurable backup manager that resides on every Network Edition Zimbra server and performs both backup and restore functions. You do not have to stop the server in order to run the backup process. You can use the backup manager to restore a single user in the event that one user’s mailbox becomes corrupted. See Backup and Restore.
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.
zimlets-network
Contains Zimlet zip files for features that are installed with the network edition.
Example of a Typical Multi-Server Configuration
The exact configuration for each deployment is highly dependent on variables including the number of mailboxes, mailbox quotas, performance requirements, existing network infrastructure, IT policies, security methodologies, spam filtering requirements, and so forth.
Figure 2 shows a typical configuration with incoming traffic and user connection. Alternate ways of configuring at many points within the network are possible.
Figure 2: Typical Configuration with Incoming Traffic and User Connections
Explanation of Figure 2 follows:
 
An external user connecting to the messaging server also goes through a firewall to the second load balancer.
The designated Zimbra MTA server looks up the addressee’s directory information from the Zimbra LDAP replica server.
After obtaining the user’s information from the Zimbra LDAP server, the MTA server sends the mail to the appropriate Zimbra server.
Internal end-user connections are made directly to any Zimbra server which then obtains the user’s directory information from Zimbra LDAP and redirects the user as needed.
 

Product Overview

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ZCS Administrator's Guide, Network Edition 5.0 (Rev 5.0.19 September 2009)
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