# DE-R-028

> If both supplier and customer are located in Germany, "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.

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/de-r-028

## Official rule text

If both supplier and customer are located in Germany, "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.