We are using Zimbra OSS 4.5.3 on Fedora 4.
It seems like Zimbra has some compatibility issues with Thunderbird.
We are having problems reading some mails with attachments sent from Zimbra.
That is, when we send out mails with attachment using Zimbra webmail, the recipients cannot see anything in the message body when using Thunderbird.
The message appears as a blank page. Have to use View->Message Source in Thunderbird to see the mail contents.
I will attach the mail here later.
Outlook is okay.