What a stand meeting allows, and what it does not
A business card handed over at a Düsseldorf stand is an invitation to talk, not a consent to marketing. §7 UWG asks for the addressee's prior express consent before advertising by electronic mail, and it makes no exception for business buyers. The safest follow-up is the one the buyer starts: a QR code on the stand that opens a WhatsApp chat with a pre-filled request.
Once the buyer writes, your team can send what was asked for, a certificate, a brochure or a quotation, in free text for 24 hours. Ask in the same chat which updates they want: order and shipment news are utility templates; new-product launches and fair invitations are marketing and need their express agreement. Record the answer with the opt-in, and the Germany guide covers the narrow existing-customer exception.
Write the templates in German, code de, for a German hospital or distributor, and in English, code en, for international buyers who visited the fair. If your buyer is one of the Japanese-owned companies in the city, ask which language it uses with suppliers before you translate anything.