According to 15 U.S.C. 7704 §5(a)(5):

INCLUSION OF IDENTIFIER, OPT-OUT, AND PHYSICAL ADDRESS IN COMMERCIAL ELECTRONIC MAIL.—

(A) It is unlawful for any person to initiate the transmission of any commercial electronic mail message to a protected computer unless the message provides—

(i) clear and conspicuous identification that the message is an advertisement or solicitation;
(ii) clear and conspicuous notice of the opportunity under paragraph (3) to decline to receive further commercial electronic mail messages from the sender; and
(iii) a valid physical postal address of the sender.

When my text-based mail client receives an HTML-only email message, it tries to render the HTML as text. It’s sometimes a jumbled up unreadable heap of garbage because the HTML is malformed and relies on a forgiving/tolerant rendering engine. Even when the HTML is proper and standards compliant, links are not exposed to text rendered. E.g. a msg will say “to unsubscribe and stop receiving emails, update preferences here.”

Where is “here”? That is just raw text. Sure, an advanced user can do a number of things to dig up that link. But I doubt that would pass the legal standard of “clear and conspicuous”.

Anyone have confidence either way whether HTML-only spam is legally actionable on this basis?