Where is the bit of my posting that says that:
Zimbra gives you the community software which is the same as the paid one except it contains little features for free?
Kopano gives you the entire stack out of the main branch and if you want the production releases you call them up?
The net result for an unpaid user is a tradeoff of features vs releases.
For a paid user the net result is the same other than perhaps you choose the one that looks best for you?
At the end of the day that's the summary.
You do not need all the advanced features by the look of it therefore you can stay with Zimbra.
I can't as I need the full product.