I've been using Zimbra for quite a while. I decided to use it to start sharing briefcases with people whom do not have an account on the server. It seemed like a valid solution but I have the following issues.
1. This one is probably the most annoying... When an external user access a briefcase they get a standard looking web page. It is very clean and I don't mind its look at all, BUT, when a Briefcase is shared that contains subdirectories I found that every time an external user clicks on a subdirectory within the briefcase, Zimbra forces a new window to open. If they decide to go back a level using the list at the top, another browser window opens. If anybody knows the best way to fix this to where it allows browsing within one tab/window... then I am all ears. I've looked for quite a while now and was unable to find a solution.
2. It would be nice to be able to maintain a list of external users at some level, whether it be administrative or user. It seems as though you only need to add the external user's password once (ex: you share a Briefcase with an external user... then that password works for all Briefcases shared to that external user). I've tested this out and that seems to be the way it works. It would be nice to just maintain the password for the external user somewhere (maybe the contacts list?) in order to do things in one shot.
3. I'd give anything in the world for the external users to have the ability to use an ajax interface like the one that is within the web client itself instead of the basic interface jetty uses.
Overall Zimbra seemed like the solution I was looking for to share pictures and videos of my family, but the fact that it opens a browser window every single time you click on a subdirectory turns it into a major turnoff. If anybody knows something I missed then please let me know.