I am having the same problem - sort of, as since the it has gone a little worse. I wasn't able to set up yahoo email accounts, nor pop3 accounts. Then I tried my gmail account and it worked!!! I am sure that the yahoo account details were entered correctly, as well as the pop3 account details. I would have thought that with Zimbra being a Yahoo product, Yahoo accounts should work - they don't but Google does. Strange!
Anyway, I mentioned that things got worse since ... now if I try to start Zimbra I get the following error:
HTTP ERROR: 500
com.zimbra.common.soap.SoapFaultException: auth credentials have expired
ExceptionId:btpool0-0:1220816952623:73b454c586a59b19:SoapEngine364
Code:service.AUTH_EXPIRED
RequestURI=/zimbra/
Caused by:
javax.el.ELException: com.zimbra.common.soap.SoapFaultException: auth credentials have expired
ExceptionId:btpool0-0:1220816952623:73b454c586a59b19:SoapEngine364
Code:service.AUTH_EXPIRED
As this is a http error, I assume that Zimbra actually installs a local web server in order to function (I am completely new to Zimbra, just thought I try it as it handles email, contacts and calendar in one package - which Vista does in a way but I had too many problems with the Vista applications). I have a local web server installed anyway, so is there a conflict with this ... shouldn't be, as it should not have worked in the first place. I know the program is still in beta stage and I hope we get a realease version soon - it really seems to do what I need ---- HELP ---- would be great if I could get it working!!!
NOTE: The HTTP error is now gone (after a restart) - the connection to Yahoo and pop3/smtp servers still doesn't work.