Wildcard SSL certificates can cover one main domain name (www.domain.com) and an unlimited amount of subdomains (mail.domain.com, login.domain.com, test.domain.com, etc.).

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What is the difference between Wildcard and SAN/Multi-Domain functionality? What is Multi Domain Wildcard SSL? What is a Multi-domain or SAN certificate? How many domains can I secure with a Multi-Domain SSL Certificate?