DE-R-028: "Seller contact email address" should contain exactly one…

StandardPeppol BIS Billing 3.0 country rules (NL, DE, IT, SE, DK, NO, GR, IS)CountryGermanySeverityWarning: the invoice is accepted but should be correctedSyntaxUBLBusiness terms

BT-43 Seller contact email address

Applies toOnly when the seller (or for some rules the buyer) is in the named country: the rule is triggered by the country code of the party. Dutch rules implement NLCIUS, German rules the XRechnung requirements inside Peppol.

Official rule text

[DE-R-028] "Seller contact email address" (BT-43) should contain exactly one @-sign, which should not be framed by a whitespace or a dot but by at least two characters on each side. A dot should not be the first or last character.

Why this error occurs

The value is present but does not match the required pattern: wrong date format, an IBAN with a wrong check digit, an e-mail address without a valid structure, a URL without scheme, or a text with forbidden characters.

How to fix it

Correct the value so it matches the format named in the rule: dates as YYYY-MM-DD in UBL and YYYYMMDD with format="102" in CII, IBANs without spaces and with a valid checksum, e-mail addresses with exactly one @, URLs starting with http:// or https://.

What the validator checks

Checked element (context):

UBL

(/ubl-invoice:Invoice/cac:AccountingSupplierParty/cac:Party/cac:Contact | /ubl-creditnote:CreditNote/cac:AccountingSupplierParty/cac:Party/cac:Contact)[$supplierCountryIsDE and $customerCountryIsDE]

Test (XPath):

matches(normalize-space(cbc:ElectronicMail), $XR-EMAIL-REGEX)

Check your invoice

Drop your XML or PDF on the validator and every failed rule is linked to its page here. Free, no account, the file is not stored.

Check your invoice →

Same check via API:

curl -F file=@invoice.xml https://einvoicechecker.com/v1/validate

Related rules

DE-R-007 The element "Seller contact email address" shall be provided
DE-R-001 An invoice shall contain information on "PAYMENT INSTRUCTIONS"
DE-R-002 The group "SELLER CONTACT" shall be provided
DE-R-003 The element "Seller city" shall be provided
DE-R-004 The element "Seller post code" shall be provided
DE-R-005 The element "Seller contact point" shall be provided
DE-R-006 The element "Seller contact telephone number" shall be provided
DE-R-008 The element "Buyer city" shall be provided

Frequently asked questions

What does DE-R-028 mean?

DE-R-028 is a peppol national rule: "Seller contact email address" (BT-43) should contain exactly one @-sign, which should not be framed by a whitespace or a dot but by at least two characters on each side. A dot should not be the first or last character.

Will my invoice be rejected because of DE-R-028?

No. DE-R-028 is a warning: the invoice is accepted but the recipient sees the notice. Fix it anyway, warnings often become errors in later rule versions.

Which formats does DE-R-028 apply to?

Only when the seller (or for some rules the buyer) is in the named country: the rule is triggered by the country code of the party. Dutch rules implement NLCIUS, German rules the XRechnung requirements inside Peppol. Syntax: UBL.

Source: Peppol BIS Billing 3.0.20 national rules (November 2025). Catalogue generated from the official rule sets on 2026-10-15.

DE-R-028: "Seller contact email address" should contain exactly one @-sign, which should not be…