Error
Error in IMAP command FETCH: Invalid messageset.
Cause
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 DoveCot email servers, you can find its documentation here.
Internally, each IMAP message is assigned a unique ID called UID. MigrationWiz retrieves UIDs from the source server to implement fast data retrieval and also from the destination server to prevent the creation of duplicates when performing multi-pass migrations. In some IMAP implementations, this bug is the reason why MigrationWiz is unable to retrieve UIDs from the IMAP server.
Resolution
Upgrade the IMAP Server
Consider upgrading the IMAP server to a version that contains a fix for this well-known bug.
Disable Duplicate Detection
If the IMAP server cannot be upgraded, and the IMAP server reporting the error is the destination server (not the source server) for the migration, the following workaround can be used:
- Sign in to the MigrationWiz account
- Click Mailbox Migration.
- Click Migrate Mailbox.
- Select the Mailbox Connector.
- Click View Mailboxes.
- Select your Mailbox.
- Click Edit Mailbox.
- Click Show Advanced Options.
- Check Do not search destination for duplicates.
- Click Save.
Important
The same Advanced Option can also be set on the connector. In this case, the setting will apply to all mailboxes under this connector.MigrationWiz stops fetching UIDs from the destination server by disabling the search for duplicates, as a result, the error is not encountered.
Note that duplicate prevention is still in effect, but only as long as the same mailbox object is used. For example, if multiple migrations are performed using the same MigrationWiz mailbox record, no duplicates will be created. However, we cannot guarantee protection against duplicates if the MigrationWiz mailbox record is recreated.