Why "unknown" email addresses are created after migration to Shopify?

During migration of Customers to Shopify, Cart2Cart will automatically generate new default email address if customer email on the Source cart is invalid. The same default email will be created during the migration of Orders, if they are not linked to particular customers, and were made by guest users - not registered customers.

The automatically generated customer emails will look like this:

Why "unknown" email addresses are created after migration to Shopify?

Posted in: Shopify