Help please.

I've recently installed Zimbra M2 and been trying to move/upload/migrate my old mail to my mailbox. So far any method used: draging and droping my old messages from a local copy using Thunderbird, even installing Courier-IMAP uploading my messages there and syncing them using imapsync (with --syncinternaldates) resulted in email sorted fine on my IMAP client (Thunderbird) but with all messages dated as today+time of upload/sync in the web interface.

My question is: is there a method in Zimbra to display messages properly (by time received) in Zimbra's webmail?