"Email subscription" refers to signing up for a service or website's updates or newsletters through email. This means you receive regular emails with news, information, promotions, or other content from that service or website. Full definition
He understands a large email subscription list is vital to authors, who use it to keep in touch with fans, make special offers, and announce new releases. (killzoneblog.com)
One other thought to add is that social media may be used to deliver some value / benefit in exchange for email subscriptions. (janefriedman.com)
This option is mandatory in order to win, but you can cancel your free email subscription at any time. (fkbt.com)