What it means
When the seller and the buyer are both in Germany, the email address of the seller's contact (BT-43) should have a single @. The @ should have at least two characters on each side, and these should not be a space or a dot. The address must not begin or end with a dot. An address with only one character before the @ fails for that reason.
Why it matters
The contact email is where the buyer sends questions about the invoice. An address in the wrong shape may bounce or be rejected by the buyer's systems. The file is still accepted, so nothing is blocked.
How to fix it
Open your company settings or the contact person in your invoicing software and retype the email address. Look for a space at the start or end, which often comes from copying and pasting, and for a second @ sign. Also check for a dot right next to the @ or at the start or end. Use one plain address, not two addresses separated by a comma or semicolon.
The rule as published
Read the rule on the publisher's site
Business terms: BT-43
Where this rule applies
| Rule set | Version |
|---|---|
| Peppol BIS Billing 3.0 (invoice) | 2026.5 |
| Peppol BIS Billing 3.0 (credit note) | 2026.5 |
Check your file
Drop your e-invoice to see whether DE-R-028 still fails, and which other rules do.
Related rules
- BR-DE-7 Seller contact email is required
- BR-DE-28 The seller's email address should be well formed
- BR-RO-L1006 Seller contact email must be 100 characters or fewer
- DE-R-007 A seller email address is required between German parties
- DE-R-030 Direct debit needs the seller's creditor identifier
- DE-R-031 Direct debit needs the buyer's account to be debited