Export / Import and matching by Mautic contact ID?

We are using Mautic also for sending postal mail - where we have no e-mail in use. Thus I want to export and import contacts, matching them by Mautic ID. While exporting with ID works, there seems to be no way to match it when importing.

Is this true or did I miss something? Would I need to assign a custom field with own unique ID for import and matching records? Shouldn’t I be able to use the the very unique Mautic contact ID?

As workaround I now created another unique ID field. I found no way to make use of the very useful Mautic contact ID, which is automatically assigned and unique by definition (much better).