In case you missed it, Yahoo announced recently that it would release all email addresses that have remained inactive for the past 12 months so new users could grab them. This will take place on August 15. The idea is to give users a chance at a simpler email address that someone else may have claimed but isn't using--and to generate some attention for the service as Google and Microsoft add such features as free online data storage and other capabilities.

Why It Matters

Here's why you should care, even if you don't use Yahoo and don't plan to: If you ever send out marketing or other email blasts, Yahoo's move can really screw you up. For one thing, during the 30 days between July 15 and August 15, messages sent to any of the emails that are due for release will bounce. So if you haven't sent out a marketing message since July 15 and you send one out now, you may have a much larger number of bouncebacks than usual.

That should worry you, says Brad van der Woerd, director of deliverability for the email marketing platform Yesmail. "With major Internet service providers, if you mail to them and breach a 10 percent bounce rate within 24 hours that will create a problem. They may block your ability to send mail to their users. And any bounceback will negatively affect your reputation." A bad reputation can result in your messages going straight to spam.

How big a difference will it make? Keep in mind that despite Gmail and Hotmail gains, Yahoo is still a very big player. Van der Woerd says a typical B2C company's email list is about 30 percent to 40 percent addresses. Yahoo isn't saying what percentage of its addresses are up for release, but given Yahoo's long history (in Internet terms, anyhow) and the ease of creating and then abandoning email addresses, it's easy to imagine that 10 percent or more of its addresses could be going up for grabs. If yours is a typical B2C email list, that could result in four extra bounces for every 100 emails you send.

Waiting till after August 15 to send out email marketing won't help you. You may see fewer bouncebacks, but that might not be a good thing. Some of the Yahoo addresses in your list will now have new owners--owners who never opted in to your emails and may have no interest in your products. That can lead to your emails being reported as spam and your domain being blacklisted by ISPs.

Even if that doesn't happen, the likelihood that those users will actually open your emails is low. And that can spell trouble too. "If you're sending emails to a high percentage of recipients who aren't opening them, it can damage your reputation as a marketer and may eventually lead to your messages landing in a spam folder," van der Woerd says.

What should you do? Here are four steps that will help:

1. Send a confirming email to all email addresses that haven't opened your emails in more than a year. "You'll have the opportunity to receive the bouncebacks and remove those subscribers," van der Woerd says.

2. Make sure you have clear and simple unsubscribe instructions in your message. Of course, you should always do this, but it's especially important right now because Yahoo may solve the problem for you by unsubscribing old email addresses from your list. During the 30 days before old addresses are released, "we're going to unsubscribe the inactive accounts from as much commercial email as possible," according to a statement Yahoo released to the press.

Yahoo is estimated to have more than 280 million email accounts according to analytics company comScore, and if I'm right that 10 percent of them may be more than a year out of use... well that's an awful lot of unsubscribing. I'm not quite sure how they're planning to get it done and they're not saying. (A Yahoo spokesperson contacted for this piece would only provide the company's general statement.) So I wouldn't count on this to happen, but it might, and if it does it'll help you.

3. Set your bouncebacks for "once and out." When you send your test email to the inactive Yahoo addresses on your list, set your system to eliminate any that bounce the first time it happens. That will clean the bad addresses off your list quickly.

4. Clear old email addresses off your list. If someone hasn't opened or interacted with one of your emails in a year, is that really a viable customer? Chances are no, and your list would be better off without that address, whether it's a Yahoo one or not. Indeed, cleaning your email list of unresponsive names at least once a year--"email hygiene"--is a good idea because it will preserve your reputation and keep you out of spam filters.

And those companies that have done that all along, "They don't have much to be concerned about," van der Woerd says.