Since the OP wants to complain but can't be bothered to do anything about it, I've submitted
Bug 37496 - Searching for specific size message does not work
Of the things mentioned, that's really the only bug, ie something that doesn't work as intended because of a programming error. The others are simply features that work as programmed, but maybe not as you would expect or prefer. You can file RFE and you can even vote to help prioritize attention for those.
The other two items point out problems with Zimbra, but they don't indicate lousy programmers or no QA. The first is a problem of maturity. Zimbra Collaboration Suite is just over three years old. They have not yet progressed to the point where everything is as complete and consistent as it needs to be. Progress has been rapid, but there is still work to be done.
The second is that sometimes Zimbra lets their own point of view on the way email should work dictate what features they implement or how. On the column sort question, some within Zimbra might respond (as they have in bugzilla) that users should use search instead of sorting. While it really is a better way to find email than scrolling through sorted messages, Zimbra should give users what they're accustomed to first. Then they can make searching so simple, obvious, and compelling that they'll discover that it's better on their own.
They've had similar blind spots with things like message priority and return receipts. To date this hasn't hurt them much because their rich web client has trumped such concerns in markets like education and SaS. But they'll have to overcome their tunnel vision if they're going to continue that success into the business market.