In a multiple-advertiser email, a single advertiser can assume the role of sole “CAN-SPAM sender.” The Final Rule issued by the Federal Trade Commission establishes that, when there are multiple advertisers in single email, a single advertiser can assume the role of sole CAN-SPAM sender if (a) the advertiser meets the requirements of “sender,” as defined under the CAN-SPAM act of 2003, (b) is the only advertiser identified in the “from” line, and (c) complies with all of the other original sender requirements imposed by the Act, including the requirements surrounding a “valid physical postal address.”
Senders must provide recipients with an easy, unburdened way to unsubscribe from a commercial email. Specifically, the Federal Trade Commission requires advertisers to allow consumers to opt out of subsequent commercial email messages from that advertiser without requiring payment, information beyond the consumer’s email address, “or any other obligation as a condition for accepting or honoring a recipient’s opt-out request,” including requiring a consumer to visit more than a single Internet Web page.
“Person” will be defined, for purposes of CAN-SPAM, as an individual, group, unincorporated association, limited or general partnership, corporation, or other business entity.
A “valid physical postal address” has been defined as “the sender’s current street address, a Post Office box the sender has accurately registered with the United States Postal Service, or a private mailbox the sender has accurately registered with a commercial mail receiving agency that is established pursuant to United States Postal Service regulations.”

In a nutshell, all the places that are using preferences pages to manage your subscriptions need to redo their processes. This is going to be huge for places such as online newspapers.