Use an e-invoicing network like Peppol for receiving and sending. This ensures a few things are really well taken care of. Consider the End User Identification requirements for registering on the network. This way, you always know that the sender of the invoice has been verified and is indeed allowed to send the invoices. Additionally, only invoices that meet the invoice requirements may be sent on the network. Of course, the invoices must also comply with a network-described and validated invoice standard. This way, as the recipient of the invoice, you know for sure that the sender exists and that you can submit the invoice error-free.
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