Some of the requested messages no longer exist: This error is caused by a well-known bug in the IMAP implementation used by your email server. This typically affects IMAP servers known as Scalix email servers.
Internally, each IMAP message is assigned a unique ID (UID). MigrationWiz retrieves UIDs from the Source server as a way to implement fast data retrieval. Because of the bug in some IMAP implementations, MigrationWiz is unable to retrieve UIDs from the IMAP server when a folder contains corrupt items.
Upgrade Your IMAP Server
Consider upgrading your IMAP server to a version that contains a fix for this bug.
Repair Mailbox Content
Consider using the following command to repair mailbox content: onscan -Avfx -U "John Doe".