Cloudiance zMailCloud webmail client issue: blank email (often displays normally in other email clients)
Note: this issue should be resolved in future releases of the web client, currently impacts at least all versions of Zimbra 8.
To see if this fix may help you resolve the issue, try forwarding the email, even to yourself, see if the body is viewable. It should also be viewable in plain text. Assuming both these are true, we may be able to resolve the issue once you report it. Please submit a ticket.