Hello Adam,
Great piece of feedback! I'm replying to each item separately. There are indeed ways to do what you want, but in a slightly different way. We love to hear whether our approach works for you or if you still see room for improvement.
Adding a "Reverse selection" to the Details' context menu is certainly a possible refinement, I'll add that to our list.
Note that you can use the Cluster Map to your advantage here: search for all items, search for all tagged items, and you see the overlap and remaining items visualized. Also sorting on the Tags column will put all untagged items at the bottom, though that works less well when you are using multiple tags.
You are right, with keyword search all senders and receivers are put together in the same document field. We plan to add advanced search abilities to the Email Address facet, like sorting on name or email address, grouping by host, etc., that will help to some extent. Having that same capability in keyword search makes sense though.
Besides using the Cluster Map, you can also use the Exclude option in the Tags facet: select the tag, click on the arrows in the Search button and choose Exclude. Any search results will then be filtered. Query results will be updated immediately, though you will have to click in the Cluster Map to force the Details table to update.
I see your point. The closest you can get now is by clicking on the column header(s) to sort on those columns. The items that you are interested in are then adjacent at the top or bottom of the list.
This is indeed surprising. Are you able to show us a (redacted) screenshot that shows this? Perhaps we can then see how this happened.
Many thanks for your feedback, we greatly appreciate it!