While I laud SmarterTools' efforts at producing a radically different product UI in this version of SmarterMail, During this transition the factors important in making an economically viable product have been lost.
When I surveyed enterprise mail software several years ago, I choose SmarterMail over the possible alternatives as others have. Up until recently every new release which sometimes resulted in a short hiccup brought about a better product.
With SmarterMail 16.x there has been a regression all around in responsiveness, features, and reliability:
1. SmarterMail UI is still slow and unusable in many browsers which have large market shares, i.e. Firefox.
2. I won't list all the features that have been removed as others have already done so. Just to note that the general usability is less than previous versions, i.e. drag drop, moving messages, RSS feeds, calendar making etc.
3. Reliability - While the server has not crashed, each new release seems to introduce some bugs which were not there previously. Example, is the bounce back with delivery which I have also seen.
What want wrong? There was an extensive beta period, and many of these issues should have never made light of day in an Enterprise product.
If I was a prospective customer and was testing this software currently, I would have to reject it. I don't consider rolling back to 15.x a viable option either since this seems to be the path SmarterMail is taking. The longer these issues take to get resolved, I believe will have an impact on both future customers revenue and current customers loyalty.