Mail-activity.nos-jd.163yun.com is a subdomain under the 163yun.com cloud service operated by NetEase, one of China's largest internet companies. This type of domain is typically used for backend or internal services — not a consumer-facing website. That explains why there's no about page, no contact form, and no legal documents: it's an API endpoint, not a store or a service you'd sign up for.
From a security standpoint, the subdomain passes all major checks: a valid SSL certificate from DigiCert, no blacklist entries, and nothing flagged by Google Web Risk. The WHOIS lookup returns no direct match, which is expected for subdomains and not a sign of concealment.
If you're wondering whether mail-activity.nos-jd.163yun.com is a scam, the answer is almost certainly no — it's just a piece of cloud infrastructure. There's no reason to trust or distrust it as a consumer because it's not meant for you to interact with directly. If this URL appeared in an email or link, be aware that it's likely part of a legitimate NetEase service, but as always, exercise caution with unsolicited links regardless of the domain.