For customers who need their subdomains (somesubdomain.domain.com) to be accessible using a www alias (www.somesubdomain.domain.com):

• Plesk/Linux: This feature is not supported Linux hosting
• Plesk/Windows: This is suppported on Windows hosting plans, but requires submitting a support request for manual change. Simply  submit a support request asking for www to be added to your subdomain (and provide the subdomain name).