Zimbra Web Client offers two options to view your mail messages.
Traditional view
Conversation view
If you are using the Conversations View feature, the default view is by conversation. To change views for this session, click the arrow next to View in the box above the Overview Pane. To change the default view, go to the Options, Mailbox tab.
The traditional view displays a list of messages with the most recent message displayed first. Unread messages are shown in bold. The information displayed on the one line includes, flags, tags, from, attachment presence, subject, folder location, size of the message, including attachments, and the time the message was received.

Conversation view displays your messages grouped by subject. The number of messages in the conversation is displayed in parentheses after the subject. Each conversation consists of the original message and all replies. Conversations containing unread messages are shown in bold.

Double-click the conversation to display the messages within the conversation. Click on a message to display its contents.
All messages related to the conversation are displayed, even if the messages are stored in other folders. The Folder column shows the folder where the message is stored.