How do I send my tax return to the Luxembourg tax authority?

You will have two options to send your forms and files/supporting documents to the Luxembourg tax authority (at the end of the questionnaire):

by postal mail – in this case, you will need to attach a copy*;
or via the MyGuichet.lu portal. In this case, you will need to attach them manually on this portal.

*If you choose to send your documents by mail, the mailing address is at the top left corner of your myTax-generated form.