European buyers are privacy-aware. Outreach that is relevant, transparent about who is writing and why, and easy to opt out of builds trust; outreach that is not damages your brand and your deliverability.
Good practice starts with relevance: contact people whose role plausibly relates to your offer, and explain why you are reaching out. Keep data to what is needed and keep it accurate.
Always make opting out easy and honour it immediately across every channel and tool you use.
Rules differ between countries and between business-to-business and consumer contexts, so legal advice for your specific situation is always recommended. This article is general information, not legal advice.