I have used a Thunderbird Add-on / Extension called MailRedirect to put a load of pop and IMAP emails back onto the server so that I can download them again using Zimbra Desktop.
This seems to have worked well. All the emails have been downloaded and the header info is as per the original, including the date sent. However, Zimbra Desktop lists emails by the date received; Is it possible to change this so that emails are listed in order of date sent instead?
Many thanks for your help.