Move from one mail alias to another

Hi,

When I backup and restore the same account everything works like a dream. However I want to merge backups from several accounts into a new account.

For example backup:

me@mydomain.com
wife@mydomain.com

Restore to:

archived@mydomain.com

Using google domains of course.

However the backup tool disconnects consistently with a network error, retries to connect and repeats. But no mail is restored.

Anything I'm overlooking?

Do I need to change the mail headers to do this?

Thanks.

Frans