imapsync (just search)
User Migration - ZimbraWiki freshmeat.net: Project details for imapsync
Users can import/export .ics for calendars & .csv for contacts from the web-client. (in versions 4.5.6 & prior see options tab, in v5 betas that has been renamed preferences)
Even easier, search REST & CURL in the forums - some key docs on it:
http://www.zimbra.com/blog/archives/...st_update.html http://www.zimbra.com/blog/archives/..._via_re_1.html http://www.zimbra.com/blog/archives/...st_and_no.html
The CLI Zmmailbox will also help you out.