Re-installation never solves a problem, it only works around it.
Make sure that the host has a valid DNS A and MX record:
To check the A record:
-you should get the ip address of the zimbra server
# nslookup mail.exampledomain.com
To check the MX record:
-you should get the ip address of the zimbra server (note the trailing period ".")
I noticed in your post that the server name was set to fedora.xjtuse.edu.cn, however, that doesn't resolve on my end (says invalid domain). Is xjtuse.edu.cn a valid internet domain? My guess is it only existed in your /etc/hosts file.