Abandoned or inactive addresses can waste your money and harm your sender reputation. Take these three steps to trim the problem areas while leaving healthy segments intact.

Here's how to tell if your email list has the winter blahs:

• Your opt-ins are growing, but your open and click rates are plummeting faster.
• You bounce more email every time you send.
• More than half of your list hasn't opened or acted on a single email in the last six months.

If the above statements can be said of your email list, it's time for you to do some judicious pruning. It might seem counterintuitive to hack off a big chunk of your list to make it perform better, but remember: Your email list is a living, growing thing, just like a rosebush that you have to cut back every year after the growing season ends.

One year, I skipped this winter pruning. That spring, my rosebushes produced tiny flowers, deadwood, and an infestation of rose scale.

In the same way, a diseased segment -- your inactives, for example -- can drag down your email list, bottoming out performance and wasting the money you spend to mail messages to abandoned or inactive addresses, especially if you pay a cost per thousand.

Consequences: Wasted money, deliverability problems
Maybe you think this extra mailing expense is worth it if the addresses are still good. After all, those addresses aren't bouncing, and you probably paid good money to acquire them. Or, suppose you have a long sales cycle, where one purchase every two years isn't unusual. Or, you use email to build brand awareness instead of driving sales or web traffic.

Fine. But, you're still spending money that you'll never recoup on this slumbering segment of your list. Even if it costs you just a fraction of a cent per address, that cost mounts up to real money when multiplied over tens or hundreds of thousands of addresses every week or month. If you have that much slush in your budget, I can think of better ways to spend it.

Also, you have a deliverability problem.

A lot of your unresponsive addresses belong to folks who abandoned them without unsubscribing. Even though virtually bottomless web inboxes take forever now to fill up, ISPs are beginning to measure subscriber activity when determining your sender reputation.

Senders who email to engaged, active people will score higher than those whose messages go to dead mailboxes. Sender reputation is one of the most important factors ISPs use to decide whether to pass your email to the inbox, route it to the junk folder, or block it.

How to prune without clipping good wood
This three-step system will help you figure out how far back to trim:

1. Define "inactive subscribers."
Classify your subscribers into at least three groups based on activity: those who clicked at least once in the last six weeks or five email campaigns, depending on frequency; those who opened one to five times over the last three months or 10 campaigns; and those who have not clicked in six months or longer. The last group constitutes your inactives.

Next, create three list segments based on activity: actives, passives, and inactives.

Use clicks instead of opens to define segments, because the open rate doesn't always capture opens by people who read email in the preview pane, without downloading images, or on a handheld device that doesn't render HTML.

2. Send reconfirmation or reactivation campaigns to inactives.
Email your next campaign as usual to your actives. Email to your passives, too, but scrutinize their click action. Then, send your reconfirmation/reactivation campaign to your inactives.

Invite them to come back with a special offer, to update their preferences, or even to unsubscribe. Use a subject line that's distinct from previous mailings.

Move responders to your active segment. Then, send a second message to inactives that stresses the need to respond or be dropped from your list.

Move nonresponders into an inactive file, and stop emailing to them.

3. Figure out why people are going inactive.
It's not enough to cut the deadwood. You need to understand why people who opted in to your emails have since stopped responding. You don't need to wait six months or a year after opt-in, either, to jump on this.

Some email research shows activity begins to fall off as soon as two weeks to a month after opt-in. Half or more of a consumer mailing list can be classified inactive after six months.

These are common reasons:

• People's interests change, but your email content doesn't. If you make it easy for people to change their interests or preferences, your email stays more relevant.
• The email you send is not what people thought they were signing up for. Here, look at the copy you use to promote your list. Does your email content still match it? Or, someone signed up to get a promotion or download and didn't know or care that the sign-up meant they would be getting your email.
• You send too much email. Or, you don't send enough. Either problem can cause people to turn off. Don't send email more often than you promised. As well, send your first email message -- a welcome email, for example, or your first issue or offer -- as soon after opt-in as possible.
• Your unsubscribe doesn't work or is too complicated. A one- or two-click unsubscribe -- no log-in required -- is what you need here. Test-drive yours now to see how it works. Fix whatever problems you find.

Contrary to what you see in your spam folder, bigger is not better for list size. Pruning the deadwood might hurt for a minute, but the healthier list that results will take away your pain.

Wendy Roth is the senior manager of training services for Lyris Technologies.