A brief review: the open rate is typically tracked through use of a tiny invisible graphic that sits on the publisher's server. When a recipient opens the publisher's email, the tiny invisible graphic is downloaded, and each download is detected and tracked. So, if you send a mailing to 50,000 different email addresses and 25,000 unique recipients download that little graphic, the open rate for your mailing would be a neat 50 percent.

It's perfectly straightforward, right?

But upon closer examination, the email open rate is a much less tidy number than it seems. It can't tell us, for instance, anything at all about whether or not plain-text emails are being opened at the same rate. Nor will it report on the recipient who downloads his mail from a POP server, then reads it offline. Such a recipient generates what's known as a "false negative."

On the other hand, recipients using the preview feature of their email client will create confusion of an entirely different kind. In preview mode, the email will go ahead and grab the invisible tracking graphic and therefore register as having been "opened." The recipient, however, might never have really opened your email, or even glanced at it. This situation generates what's known as a "false positive."

With such falsehoods eating away at the accuracy of open rates at both ends, it can be difficult to know how much weight, if any, to assign to this number.

...and They're Becoming More Bogus

Lately, anti-spam efforts are diluting the open rate's significance even further. In an attempt to protect recipients from having to see unwelcome images-such as explicit adult materials-many major email clients are now configured to block all images by default. AOL has maintained this strategy for years, and other large ISPs are distinctly moving toward this no-image tactic.

Recipients can usually unblock images by manually adjusting their email client's settings, but the publisher is left in the dark about how many users are doing this. Until a more effective open rate system is devised, the publisher must assume that a certain percentage of the mailings are being opened without being reported as such.

With email open rates so compromised by contingencies both old and new, should we just start ignoring this embattled metric altogether? Has it outlived its usefulness?

Silver Lining in a Dark Cloud

Despite all of these uncertainties and doubts, open rates can still be useful when they're used as a general barometer of email marketing campaign success. Read in this manner, they provide a sense of how one mailing fared relative to others sent to the same group of recipients.

If your open rates are steadily declining over time, for instance, it might be a sign that some aspect of your publication has gone stale and is in need of revamping. On the other hand, if open rates are going down, but click-throughs and revenue are going up you might not care so much that open rates have weakened

In other words, eyeballs are nice, but actions are better.

That said, one particularly worthwhile way to look at open rates is to separate out your old and new subscribers. Some studies suggest that an effect called "list fatigue" is responsible for significantly lower open rates among longtime recipients of your email. If you notice a significant difference between the two groups, you might consider sending a special offer to the old-timers in order to woo them back.

In fact, if you have demographic information about your list members, it can be very much worth your while to examine open rates by gender, age, location, customer status, top domains (i.e. AOL or Microsoft), method of subscription, or other data you collect. Any significant differences that you uncover may justify creating different versions of your messages for certain segments.

The Picture: Big and Little

The abundance of high-level statistics on open rates doesn't seem to suggest that they're going away any time soon. Industry sites like Marketingsherpa.com still conduct large surveys to find out if overall open rates are up or down. Emarketer.com continues to sell quarterly reports on open rates by type of business. And in 2003, Opt-In News conducted a study to find out if open rates were higher among business-to-business mailings or business-to-consumer ones (answer: b2b)

But as interesting as these high-level statistics can be, what's usually most practical for the individual email marketers is to compare their campaign's open rates against their own internal results. This is because industry statistics can vary wildly based on a number of different factors, whereas your own in-house lists (provided they're kept clean and up-to-date) should remain generally consistent, particularly over the short-term. In this manner, your open rates can be placed in a meaningful context.

Jim Sterne, author of Advanced Email Marketing advises, "It's easy to get caught up in your stats, but the absolute numbers themselves aren't too critical. Deliveries, bounces and opens all have an unknown element to them, but what ultimately matters are changes in delivery, bounce and open rates from one mailing to the next. Keep an eye out, then, for surprising blips or interesting long-term trends."

Remember, an email open rate is like a weather barometer. It can't tell you exactly how many inches it's going to rain, but it can certainly tell you whether the pressure is rising or dropping. Open rate patterns can help to reveal the overall climate in which your campaigns are being received. Approach your open rates in this manner, and you'll filter out the noise of false stats, stress less over small changes, and have a better sense of what your email marketing program needs to be even more successful.