I'm using Zimbra Desktop on Mac OS X Snow Leopard with the Open Source version of Zimbra.

OS: Mac OS X Snow Leopard 10.6.8
Zimbra Desktop: 7.0.1 (build 10791) (current version)

I told Zimbra to play a sound and display a Growl notification evrytime an email comes.
But no sound is played and no Growl notification is displayed.
Growl is running fine and other applications use it.
The only display of new E-Mails is the number in the Dock Icon.
It shows up if new e-mails come but it doesn't get reset.
It I read an e-mail the number stays and if a new e-mail comes, one is added.
So I start the client. No number is displayed.
I get one e-mail: A 1 is displayed.
I read the e-mail: The 1 is still displayed.
I get another e-mail: A 2 is displayed, but only 1 e-mail is unread.
I read the e-mail: The 2 is still displayed.
And so on!