AOL was sued a ways back by plaintiffs who alleged that AOL improperly included advertisements in email sent by AOL subscribers.  (Previous post here.) 

Courthouse News reports that AOL has been sued again by plaintiffs who allege AOL violated the Electronic Communications Privacy Act by inserting ads in emails sent from paid accounts.  (Complaint:  [pdf].)  I haven't taken a close look, but the issue likely is that AOL inserted advertising triggered by key words, and (plaintiffs argue) in the process necessarily accessed the content of user communications.  (Does it make a difference if no human being ever read the contents of the emails?)  Here's an EPIC letter flagging similar issues around gmail contextual advertising.  (For background:  Concurring Opinions; Wired (Facebook email censorship).)  Plaintiffs asserted a few other ancillary claims such as unjust enrichment (etc.).