I am using Zimbra Desktop 1.0.4 (Build 1833) Windows version.
We found that whenever, an email attachment of a html page. All Chinese characters are showed as "?". If we save the email attachment to desktop, and then open with normal browser, all Chinese characters are showed as normal and correct Chinese characters.
It seems that Zimbra html viewer is not support fonts in unicode. Is it anyway, that we could configure the viewer in Zimbra so that we could see these Chinese characters directly.