Workarounds and complex scripts are one thing, but the long and short of this is that Zimbra needs to get this functionality into the mail code asap or risk losing customers.
New customers evaluating the product in a region where this is a legal requirement will have no option but to select a product that already offers this function.
It's not a case of selection based on extra features, is a case of selecting a product based on minimum required features. In this case, it's a forced disclaimer.
If the users can come up with a hack in a matter of hours, then I'm afraid I'm going to have to play the indignant user card and say that Zimbra should release an intergrated fix in the next point upgrade.
I'm currently an OSS user (because the zimbra sales team dont seem interested in answering my mails) so I cant demand these features, but I'm sure the Network Edition users should be able to insist on this