We at WireLoad are proud to introduce YippieMove '09 - an online email migration tool.
With this release, you can now move between virtually any two email providers/servers (as long as they support IMAP).
We've worked with a bunch of customers migrating to Zimbra, and it works great!
If you're moving a larger number of user, we can insert the data using a CSV-file.
$15 per account (volume discounts available)