Class of Service (COS) is a Zimbra-specific object that determines what default attributes users' accounts have and what features are added or denied. The COS controls mailbox quotas, message lifetime, password restrictions, attachment blocking, and server pool.
A default COS is automatically created when Zimbra is installed. You can modify the default COS, and you can create new classes of service. A COS is a global object and is not restricted to a particular domain or set of domains.
COS is used to group accounts and define the feature levels for those accounts. Each account is assigned a COS. You could, for example, create an Executive COS which is configured to enable all features, have unlimited mailbox quotas and never purges messages and create another general-employee COS which enables only the mail feature, sets the mailbox quota and purges messages every 60 days. Grouping accounts to a specific COS lets you update or change account features in block. Change the COS and all accounts assigned to the COS are changed.
If a COS is not explicitly set for a new account, or if the COS assigned to the user no longer exists, the default COS is automatically assigned.
A COS setting includes the following:
General Information tab showing the COS display name and a one line description that is displayed in the COS content pane.
Features tab listing all the features, and whether they are enabled or not.
Preferences tab showing what mail-view preferences are enabled.
Themes tab showing the default theme, installed themes, and available themes. See Defining Theme for the Zimbra Web Client UI.
Zimlets tab showing a list of Zimlets that are installed and available for the user interface. See Adding Zimlets to COS and Accounts.
Server Pool tab listing the mailbox hosts that are available to be assigned a new mailbox. See Assigning Accounts to Different Servers.
Advanced tab showing quotas, password constraints, session length, and message lifetimes, and attachment blocking use. See Account Advanced Features.
Even though a COS is assigned to an account, the COS attributes can be overridden by:
Changes end users make to their mailbox options
Global settings set to reject attachments
Individual accounts settings changed to override specific COS attributes
Important: Mailbox features are enabled or restricted for Zimbra Web Client users. IMAP and POP client users may not have the restrictions that are configured in their COS.