about how to Zimbra (Open source edition) calendars on an Android Device

I have tried to synchronize my Samsung galaxy 2 (with Android 2.3.5 version ) to the zimbra server 7.x with zextramobile installed.

The synchronization not success, no matter I configure my account according to the instruction of ZxMobile on Android Device (message shown cannot connect to server)

I have checked the account and confirmed the zxmobile was enabled. I wish to see if I miss something on the setting. Besides, I refer to the How-To and find an article suggest the synchronization on android device can carry out by using AnDal-Cal. Then, I installed it and get the synchronization done. If this is the only solution?

Regards,
Elam