Yes there is mail export, both as just eml/plain text or with metadata files as well (info like tags/flags/etc) - when you select type 'account' it's exported as a gzipped tar:
If you were asking for a particular format like PST (there's an RFE in bugzilla) OR can't find this section let us know (ZD 1.0 based on ZCS 5.x might look a little different but if using say 1.0.2+ it should be there):
There's also other ways to query REST url's (for versions before that section existed) or zip format etc.
Plus there's a few zimlets for exporting a single message to text or html or zip or tar etc.
http://www.zimbra.com/forums/announc...available.html