DE-R-028:Invalid email format. The seller contact email (BT-43) must contain exactly one @ sign with at least two characters on e
Fix: Invalid email format. The seller contact email (BT-43) must contain exactly one @ sign with at least two characters on each side, and no dots at start or end.
Invalid email format. The seller contact email (BT-43) must contain exactly one @ sign with at least two characters on each side, and no dots at start or end.
Engine Classification
Requires user confirmation before application
What is DE-R-028?
DE-R-028 is a warning validation rule defined in the PEPPOL_BIS specification (DEU national rules). It validates the ElectronicMail element under Party > Contact in the UBL invoice XML.
The invoice may pass transmission, but this non-compliance can cause problems during tax audits or buyer-side processing.
Target path: //cac:AccountingSupplierParty/cac:Party/cac:Contact/cbc:ElectronicMail
Why This Error Matters
Invoice will be rejected by German XRechnung validators. German e-invoicing has specific format requirements for payment details, contact information, and attachments.
DE-R-028 is a soft failure that can cause issues at the receiving end — tax audits, ERP processing, or VAT reconciliation mismatches.
Validator Behavior
- ·Generates validation warning
- ·Rejected by PEPPOL Access Points
- ·Rejected by XRechnung endpoints
- ·Error returned: DE-R-028
- ·Specification: PEPPOL_BIS
How to Fix It
Find the missing or empty field
Check cbc:ElectronicMail at //cac:AccountingSupplierParty/cac:Party/cac:Contact/cbc:ElectronicMail. This field is required but is either missing or empty.
Set the required value
Invalid email format. The seller contact email (BT-43) must contain exactly one @ sign with at least two characters on each side, and no dots at start or end.
Re-validate your invoice
Upload the corrected invoice to confirm DE-R-028 is resolved.
XML Example
Generic example based on the rule's target XPath. Your actual XML structure may differ.
<!-- Incorrect value --> <cbc:ElectronicMail>INVALID</cbc:ElectronicMail>
<!-- Corrected value --> <cbc:ElectronicMail>VALID_VALUE</cbc:ElectronicMail>
Technical Reference
//cac:AccountingSupplierParty/cac:Party/cac:Contact/cbc:ElectronicMailCommon Causes
- ·Seller email address format invalid
- ·BT-43 must contain exactly one @ with valid structure
- ·cbc:ElectronicMail missing @ or has invalid format
- ·Email has whitespace around @ or invalid characters
- ·Dot at start/end or adjacent to @ in email address
Seeing this in production? The API handles DE-R-028 automatically. See the fix response →
Frequently Asked Questions
Invalid email format. The seller contact email (BT-43) must contain exactly one @ sign with at least two characters on each side, and no dots at start or end.
Invalid email format. The seller contact email (BT-43) must contain exactly one @ sign with at least two characters on each side, and no dots at start or end. You can also use Invoice Navigator's compliance engine to correct this automatically in your pipeline.
DE-R-028 is a warning that may not always cause rejection, but indicates a compliance issue.
Many instances of DE-R-028 can be automatically corrected using Invoice Navigator's compliance engine. The fix is applied in your pipeline with full audit evidence.
Related Content
Last updated: 14 April 2026
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