Had some trouble with getting Zimbra SSL certs to work wth my E61. This wiki page was not completely right for some reason. Using IE and getting the (tomcat) SSL cert from the web page is also important. The tomcat server seems to have a different cert from the main CA/smtp/etc services. Not sure while.
For some reason Firefox doesn’t allow you to save a SSL cert to disk. Or at least I haven’t found the correct method.
Anyway I’ve got pop to work well with Zimbra on the E61, previously I got the Zimbra Mobile to work with a trial Network Edition version. I might try out Funambol bext to see if it works with the Open Source version of Zimbra.