Migration from one mail system to another is often painful. This can result in a user having to look in two different places to find mail, or in the worst case mail disappearing.
Copying the contents of one mail system to another often seems like a good idea, that way if anything goes wrong at least the old mail is still avaible.
Ideally you know exactly what you are going to do at the start, you move everything across and then you kill the old mail system (or at least make it not visible from Mail clients). That way users are not confused by having two sets of identical folders.
Many users think email means Outlook, this is unfortunate for a number of reasons.
Lots of different versions of outlook exist, and upgrading a whole company to the same version may cost some money, so consiqently people do not upgrade.
Microsoft have not really gone the whole way to make outlook work smoothly with imap, some have argued that they have deliberately done this. Whatever Microsofts incentive is to make users move to exchange.
Inconsistancies like, you must have a personal folder when using imap or pop and don,t need one with exchange, leave users wondering why they have two inboxs trash etc. Also the fact that the personal folder always appears first and imap at the bottom, shows that when it come to open standards Microsoft are not your friend.
THE GOOD NEWS
The Zimbra web client is adeqaute for a large number of users Thunderbird has good imap support
Existing data contained in personal folders can be saved to a PST file from within outlook then a utility is provided by Zimbra to move this data to the Zimbra server.
You need the ZCS Import Wizard see how to get this below. This does not always work 100% and you may need to be selective about what you export from outlook to the PST file before doing the import.
Just put this into your browser :-
and select the ZCSImportWiz-(version).exe download and run it.
Moving from Excahnge to Zimbra
Zimbra has two tools which exist