'Received' dates muddle in Zimbra, OK in Outlook

[slow]

I have just copied all emails from one email address (info@) to the main email address (emma@) for one of my domains, as I only want to use one account now, and although in Outlook it has collected all the copied emails into the e,,a@ account with no problems, and shows the originating 'Received' dates, in Zimbra it has given all emails a 'Received' date of right now! In the actual headers of each email it still shows the original 'Received' date, so the info is there, just not being used.

Can anyone explain to me what I might do to correct this, so the emails all go into date order according to when they were actually received - I did think this was one of the points of IMAP mail - whilst bearing in mind I have no command line experience or coding / scripting ability so I'll need it step by step if it's not a simple change in the GUI!

Many thanks