Thanks to those who helped earlier - I now have a zimbra server up and running.
Still got some problems though as follows:
Cannot access the admin console other than on the server itself - trying to access the https url from any other network computer fails.
Zimbra desktop will not connect to the zimbra server - however can login to the web client by typing the internal ip address of the server from any network computer.
No mail at all is being sent or received either internally or externally. Followed the split dns instructions carefully prior to installation but presume I have got it wrong somewhere. Mail does not bounce back and the zimbra webclient shows mail as sent.
Any advice on troubleshooting the dns issues would be greatly appreciated.
I tried to set up MTA mail relay and it wouldn't accept our isp's smtp server name - I eventually put in the ip address of the isp's smtp server.
Thanks for all assistance so far.