Perhaps nothing.
Using a news story or pop culture as a hook can create interest that attracts readers. Keep your subject line (or headline) relevant and appropriate, though, or you’ll forsake credibility.
“What will Happen to eMail Marketing on the iWatch?” is a good example, even if a horrible thought.
“What will Happen to eMail Marketing during a Zombie Apocalypse?” is not a good example. (I admit to giving it some thought but, really, there’s nothing to write about.)
photo by Sangudo / Flickr