I'm using zimbra now since the end of last year.
Zimbra 4.0.5 (debian) is installed on OpenVZ.
The load of the zimbra server is low (email for 4 people, maybe 30 emails per day)
There are a couple of things that really suck with zimbra:
1) It needs at least 2Gb of memory. My first computer (ZX81) had 1kb of memory!!!!
2) It regularly crashes and must be restarted (once per week)
3) Maybe once per month there is something locked, which requires me to fix something (e.g. virus database broken, zimbra/store inconsistency)
4) It is slow over the internet. Tried to read my emails from Seychelles (maybe 3kbyte/sec connection) and it needed 20 minutes to load all the data. What would a mail client be good for than reading mails from abroad?! All this fancy graphics are nice, but I would rather like to read my emails faster.
5) With the internet explorer zimbra needs very long to load. I know with firefox it is ok, but sometimes from abroad there is only a internet explorer installed.
6) Configuration is sometimes cumbersome, some features in the webinterface are broken and require the command line for configuration.
Anybody sharing this experience / any comments?