Invalid message sequence number: This error is caused by a well-known bug in the IMAP implementation used by your email server.
Internally, each IMAP message is assigned a unique ID called UID. MigrationWiz retrieves UIDs from the Source server as a way to implement fast data retrieval. MigrationWiz also retrieves UIDs from the Destination server as a way to prevent creation of duplicates when performing multi-pass migrations. Because of the bug in some IMAP implementations, MigrationWiz is unable to retrieve UIDs from the IMAP server.
Upgrade Your IMAP Server
Consider upgrading your IMAP server to the latest version.
Disable Duplicate Detection
If your IMAP server cannot be upgraded, and the IMAP server reporting the error is the Destination server (not the Source server) for your migration, the following workaround can be used:
- Sign in to your MigrationWiz account
- Click on Mailbox Migration.
- Click on Migrate Mailbox.
- Select your Mailbox Connector.
- Click on View Mailboxes.
- Select your Mailbox.
- Click on Edit Mailbox.
- Click on Show Advanced Options.
- Checkmark Do not search Destination for duplicates.
- Click on Save.
Note: You can also set the same Advanced Option for the project. In this case, the setting will apply to all mailboxes in this project.
By disabling the search for duplicates, MigrationWiz stops fetching UIDs from the Destination server. As a result, the error is not encountered. Note that duplicate prevention is still in effect, but only as long as you use the same mailbox object. For example, if you perform multiple migrations using the same MigrationWiz mailbox record, no duplicate will be created. However, we cannot guarantee protection against duplicates if you recreate the MigrationWiz mailbox record.