Transferring an old Hotmail/Outlook.com/Live email archive to your new gov.uk mailbox
To date, we have not found a reliable way to transfer emails from Hotmail / Outlook.com / Microsoft Live. This appears to be an issue with the credentials provided by Microsoft security which doesn't validate in the Zoho Data Migration.
We are working on a solution to this.
In the interim, we recommend setting up automatic forwarding so incoming emails get delivered to your new gov.uk domain.
Here's guidance for doing that.