A company may leverage owned media by sending sales to customers registered with its Web site.

参考译文：一家公司可能/可以通过向在其网站上注册的客户发送销售信息来利用它所拥有的媒体。 

备注：registered with its website 为形容词短语作定语修饰前面的名词“customers” 相当与定语从句 customers who were registered with its web site

registered  adj.  注册的; 登记过的; 已挂号的;

The patient was registered under a false name.  那位患者挂号时用了假名。

He asked his mother to send it by registered mail.  他让他妈妈用挂号邮件寄。