Mail, messages, etc. that you receive have the same legal effect in terms of payment, acceptance and complaint periods, etc. as if they had been received by ordinary post.
Digital Post and e-Boks are closed communications systems and require the validation of senders using a controlled digital certificate. As the recipient, you can therefore be certain of the authenticity of the message and that the sender is recognised in the systems.
When you store documents in your archive, this is equivalent to making a photocopy. Most places generally recognise a digital copy of a document as having the same validity as the original document and therefore accept digital copies.
It cannot be ruled out, however, that some places may require you to produce original documents. You should consider this before destroying any original documents. If you are in any doubt, do not destroy the original document.