I unintentionally checked the check box "Do this automatically for files like this from now on", and now all my excel attachment are downloaded instead of being opened.
I cannot find the way to undo it.
My software / OS info are: Zimbra Desktop 7.2.3 GA (build 11971) / OS X 10.9.1
I saw the posts about finding mimeType.rdf file, but I am unable to locate it on my Mac.
Thanks for your help, it drives me nuts.