That's just the file created date, if you open one of the .eml's in a txt editor you'll still see the 'Date' header intact.
Say you choose to re-import with zmlmtpinject, you run a script to add the 'X-Zimbra-Received' header.
-I'll let the seacom.it people post a link to their current zimlet.
EDIT:
Fbackup:
Zimlet Folder Backup | ::Seacom°blog°Zimbra::
&
Another approach:
http://www.zimbra.com/forums/zimlets...-txt-file.html
----
UPDATE: For 5.0.9/.10+ I highly recommend the tar formatter for personal backups to get items plus metadata:
ZCS-to-ZCS Migrations » Zimbra :: Blog
(5.0.11/.12+ has it nicely exposed to users -instead of remembering url tricks- in the import/export section of the preferences tab)
I realize the built-in import/export on newer versions takes most of the necessity of your fbackup zimlet away, but just wanted to say
thanks Anteos & lfasci for the good work you put into it!