With email marketing software becoming more sophisticated year on year you will, no doubt, wonder if there is one that is more important than all the others. I'll take an educated guess; most of those involved in email marketing would suggest that the open rate is the one essential. After all, if an email is not opened there is no chance of a sale.

There has been a suggestion that with Yahoo, iPhone and others, the open rate is no longer as dependable as it was before as these do not automatically load images and therefore many aren't tracked. This ignores the basic truth about metrics; most are comparative. The number need not refer to specific events. The metric supplies information as to the effectiveness of any change.

The delivery rate is obviously something that should be monitored with great care. If your emails are being classed as spam then you are in danger of being seen by Google as something of a liability. If your marketing email doesn't get into customers’ inboxes then the whole campaign has failed.

What those who concentrate on these various returns fail to realise is that email marketing works towards one metric, the only one that counts; completions. Everything else is subservient to it because you are in business for one reason only, that is to sell.

I’m not suggesting that every other metric can be happily ignored. For instance, if your unsubscribe rate increased after a change in email design, you can compare the rate to the segmented list that ran with the old style. As I said, it is comparative.

You are working towards one target in email marketing; the sale. It is of no benefit to you if your click through rates goes up by 4% but your completion rate drops by 2%. There is no good news and bad. It is all bad news.

Let's say that you decide to target your email at a younger demographic. You segment your list into two groups in the specific age range. You want to appear less formal so you change the Subject Line from your regular, ‘Mr Smith, we have a bargain for you’ to one less familiar but more bouncy, such as ‘Wow! Have we got something for you’. You hope to catch the youngsters with something more catchy.

If the returns show that the open rate had increased you might assume that this is the way to go with other subscribers of the same age group. But what if completions had dropped? You conclusion would then be that those who preferred the more formal form of address were the ones who were more likely to complete. There is no point in having your marketing email opened by those whom you are unable to convince to buy.

When you run comparative tests with segmented lists then the metric which you are concentrating on should not be viewed on its own. If there is a drop in completions then whatever the figure, the result is a negative.