Well, hats off to...

Avast! Antivirus Free Edition

...which caught a virus infected email message that Zimbra was synching from Yahoo! Mail. I don't recall seeing that mail in my main mailbox and Zimbra is not syncing any folders. So, I'm not sure where or when it came from. Based on the email address it might have been from the 2000-2001 time frame. But, Zimbra does not look like it has reached that far back in syncing yet. So, its origins in time may remain a mystery.