Sending invoices by email: is it allowed and how do you prove it?

Electronic invoicing is allowed, with one condition

An invoice may be electronic if your client accepts that form. That acceptance need not be in writing: if your client pays a PDF invoice without complaint, that is acceptance enough. The content and authenticity of the invoice must also be assured, but in practice a PDF you do not change afterwards is sufficient. Which details are mandatory is covered in creating your first invoice.

Note the difference with e-invoicing in the strict sense. That is an invoice in a fixed data format such as UBL, read straight into your client's bookkeeping. With government bodies that is mandatory, and more obligations are coming in Europe; see e-invoicing with UBL. A PDF is not an e-invoice in that sense, but for ordinary business clients and private individuals it is perfectly valid.

Sent is not received

As soon as a client fails to pay, the question arises whether they received the invoice. That is no formality: to claim statutory interest and collection costs, your client must have been put in default, and with a consumer you must first send a reminder with a fourteen-day period that the client actually received. The burden of proof lies with you as creditor. An email in your Sent folder is weak evidence for that.

Strengthen that in a few ways. Use invoicing software that logs when the email was delivered and whether it was opened. Send the invoice to an address the client provided themselves, for example in the assignment confirmation. For large amounts, ask for a short acknowledgement. And if you are heading towards a reminder to a private individual, also send it by post, possibly registered. More on that process is in a client who does not pay and statutory payment terms and collection costs.

Keeping it in the form you sent

You must keep your invoices for seven years, and in the form in which you sent them. If you sent a PDF, you keep that PDF, not just a printout or a line in your bookkeeping. Preferably also keep the accompanying email, because it contains the date and the address you sent it to. How to set that up digitally is in keeping receipts and invoices digitally and the record-keeping obligation.

In practice that means: have your invoicing software archive the sent PDFs, or keep them in a folder per year with the invoice number in the filename. That way, if the tax authorities or a client asks, you can retrieve the original invoice within a minute, with its send date. Sequential numbering helps enormously; see invoice numbers and the rules.

1. Ask every new client for their invoicing address and record it in the assignment confirmation.
2. Send from software that logs delivery, not manually from your mailbox.
3. Keep the sent PDF plus the accompanying email, for seven years.
4. Also send a reminder to a private individual by post, with a fourteen-day period.

Practical problems you can avoid

The most common cause of an unpaid invoice is simple: it ended up in the spam filter or went to an address nobody reads any more. Large clients often work with a central accounts payable address or a portal where you have to upload the invoice; if you send it to your contact person, it will sit there. So ask at the first assignment how invoices should be delivered, and whether a purchase order number is required.

Also never send only a link to an invoice without an attachment. If that link later disappears, you can no longer supply the invoice in the form you sent. And check your sending address when you move to a new mail environment: bounced invoices sometimes go unnoticed for weeks, letting your payment term slip by. A fixed rhythm for chasing debtors catches that.

Frequently asked questions