Hello, welcome.
You should also try to ask your question in English and your native language, you might get some mother tongue answers 8)
If you want to use it for your company (no resell, etc), you still have two possibilities.
Either the OpenSource Edition version fits your need (no official support, no hot backup, no domain delegation, no Outlook 2003 connector, etc) and you can use it.
Either you need one (or some) of the Network Edition features. Then you'll have to buy some yearly licences. The NE by itself is actually two differents licence levels : Standard and Professionnal. The Pro allows you to use the Outlook 2003 connector (ZCO) that you won't find in the Std.
If I'm not clear enough, I think you should contact
sales@zimbra.com or find a VAR to answer more precisely to your questions.