This setting is an option under the Advanced tab of an account or COS, but I haven't been able to locate a clear description of what it means. Does it mean that only the "download" and "add to briefcase" options are available for the attachement?

What about "Disable attachment viewing from web mail UI"? When I tried this, it seemed to give the user the same options as "Attachments can be viewed in HTML and their original format".

This is a new test setup, zmcontrol -v output is Release 5.0.16_GA_2921.RHEL5_64_20090429021719 RHEL5_64 NETWORK edition.