Hello. We are migrating, via our provider, from a Linux imap server to a Zimbra NE install. The main thrust of the migration will be a couple of imapsyncs. One a couple weeks in advance and then another one when the actual migration occurs. We have read the migration docs, but are confused about how to handle our situation. Like many places, we have a split of webmail only users and fat client users that may or may not leave mail on the server.

1. Some users use fat clients (Outlook, Eudora, and Thunderbird). Users mostly keep mail on the server, but they control that option themselves to stay under quota. We will sync their old email to the Zimbra server. My concern is that once they connect to the Zimbra server their fat client will download all of their messages again. The email client will see the connection as a new server and download all of the old messages. This is unacceptable, as it would result in thousands of duplicates for some users. How do we avoid this? Everyone seems to be using imapsync with Outlook. Are we missing something here? Some of our users have huge mailboxes.

2. Some users use webmail only. They should be fine after the imapsync.

Thank you.