In Zoho Mail, the emails that are a part of the conversation are listed with a conversation icon in the listing. You can click the icon, to view the entire thread of conversation in the conversation or threaded view in a new tab.
Generally when emails are replied or forwarded, they are linked with the original message using some entries in the header and based on that a conversation is generated. The conversation view lists the messages in the order they were received.
The message tree indicates the flow of messages on how the entire conversation has unfolded, and each message in the thread is linked with the previous message . You can navigate through the entire conversation easily from the preview pane. You can add a label to all the messages in the conversation using 'Label entire thread' option.