In baseball, if you succeed three times out of 10, you’re an All-Star. It’s the same in e-mail marketing.

On average, only about one in four e-mails sent out by a marketer is actually opened by a consumer. And that’s not just for random blasts; that includes e-mails sent to lists of customers who have signed up to receive them.

The crucial element in a marketing e-mail is the subject line. A great deal of study has been devoted to analyzing what makes a good subject line. Not surprisingly, the rules of good subject lines are like the rules of good writing: shorter is better, and active words are better than passive.

A lot of testing has also gone into the design of e-mails, with eye-tracking studies and “heat maps” showing which elements of the e-mail body readers pay most attention to. It’s pretty clear that readers pay most attention to the information near the top of the e-mail, then start skimming as their eyes move down the page. This holds true whether there are visual images in the e-mail or it’s all text. So marketers are well-advised to put their strongest material up top. If you save it for a big finish, you’re probably wasting your effort.

At Fast Horse, we’ve been handling an e-mail program for a client that has seen open rates in the mid-to-high 30 percent range, a Joe Mauer-like performance. I won’t take credit for that; I think our client has a strong mailing list and a superior product that people want to learn about. (Send me an e-mail, and I’ll tell you about it.)

But big changes are brewing in the e-mail world. The current models are based on an audience that’s sitting in front of a desktop or laptop computer. But more consumers are getting their e-mail on smartphones. This change is going to force e-mail marketers to rethink how they deliver their messages, possibly sending only a compelling subject line with a link to a website where the rest of the information will reside.

And, of course, Google is getting ready to roll out a game-changer. (Is there any area of the information world that Google can’t effortlessly dominate?) The information colossus last week gave the world its first peek at Google Wave, which is being billed as the e-mail of the future.

Google Wave, set for official release later this year, combines e-mail and instant messaging with rich text, graphics and photos. To me, it sounds less like something completely new and more like a wiki on steroids.

But with the weight of Google behind it, most of us will doubtless be catching the Wave by this time next year. And then we’ll have to develop some new measurement standards to decide who’s staying in the game and who’s going to spend the All-Star break at home.