customer without email address

Private persons do not necessarily need to receive an invoice.
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It may not always be necessary, but since materials are sometimes installed that come with a warranty, it is desirable. That's why I wanted to know if I can create an invoice here, print it out, and then simply send it by mail. Furthermore, sometimes it concerns higher amounts that we are not (allowed to) accept in cash.

Yes, if he does not have email, you can only deliver the invoice to your private person by mail or when placing the goods.