Are you looking to secure one main domain, along with all of your subdomains? If so, then the Comodo Wildcard SSL certificate is an excellent option. With just one certificate, you can cover your main domain (www.domain.com) and as many subdomains as you need (mail.domain.com, billing.domain.com, etc.domain.com). Also, because this is a Domain Validated (DV) certificate, the Comodo Wildcard SSL can be issued in as little as a few minutes. One of the easiest and most economical Wildcard options, this certificate is perfect for small to medium sized businesses and lower-traffic ecommerce sites.
One of the most efficient certificates in the industry, the Comodo Wildcard SSL certificate will protect one main domain along with an unlimited number of subdomains. So, you can protect www.domain.com, along with mail.domain.com, sales.domain.com, subdomain.domain.com, etc.