I'll try to give you a few answers:
1. Pass-through Authentication - Don't know what this means; need more info on what you are looking for.
2. File --> SendTo with MS Office - There is a very old RFE open on the Zimbra Bugzilla for this (
12845). The status for the RFE says "Assigned" and there are 37 votes for it, which is not a huge amount, but not trivial (1 or 2) either. Hopefully it will eventually come to Zimbra.
3. Drag-and-Drop Message Editor - Currently there is a Firefox add-on that allows you to drag-and-drop files to a message which adds them as attachments. This functionality also exists with the Zimbra Desktop. There is another open RFE (
27153) to have add cross-browser/cross-platform support for this feature. This RFE also shows up as "Assigned"; it only has 5 votes, but is not nearly as old as the previous one. Again, hopefully this functionality will eventually be available in Zimbra. Note that the current Firefox/Desktop feature adds the files as attachments; it does not embed them in the message. I very rarely, if ever, compose HTML messages and try to embed files into the message. There might be a way to do this, but I am not sure.