Undeliverable emails--email "bouncebacks" or "bounces" for short--are becoming more and more of a challenge for email marketers these days.

According to a recent Association for Interactive Marketing (AIM) survey, 77% of respondents had bounce rates up to 10%, and 23% had rates greater than 10%.

Why should you be concerned? Because customer acquisition is expensive, and email bouncebacks could mean the loss of customers and prospects that you paid dearly to acquire.

First, Let's Define Some Terms:

A "bounce" is where the proverbial rubber meets the email. This happens when a recipient's mail server rejects your email message.

A "soft bounce" is often a temporary problem, thus the descriptive adjective "soft." It happens when the mail server confirms the recipient's email address, but even so, cannot deliver the message. The recipient's mailbox may be full or inactive, the recipient's mail server may be temporarily down, or the connection may have been broken.

A "hard bounce" is a message that's permanently undeliverable because the address is non-existent or invalid, or because the recipient's mail server is blocking your mail server.

Why So Many Bounces and What Can You Do About Them?

* Email address churn in your house list. People change ISPs, jobs and email addresses at random. Often you'll be the last to know. Some email address churn is normal. But the erosion of your house list can impact your bottom line in seriously negative ways.

What can you do? Check with sales, support or someone on the front line in your company, and follow up by phone or by snail mail to recapture valuable customers and prospects.

In addition to your unsubscribe or edit interests link in your email, consider adding a note saying, "If you plan to change email addresses, or if you prefer to receive this newsletter at another address, please email us."

Remember, it is seven times less expensive to market to an existing customer than it is to acquire a new one. The effort will be well-worth your time.

* The use of free email accounts. Many people who use free email accounts do so as a secondary mailbox. As a result, they do not check their mailbox often. Free email accounts, and some paid accounts, can hold only a limited amount of email, so many times newsletters and advertising email will bounce back as undeliverable.

What can you do? You can try the same techniques as above and, assuming you have the recipient's permission, you could use snail mail to obtain their new email address. Try sending a postcard asking them to revisit your site to update their profile. The postcard should include a URL leading to the profile update area of your site.

* Spam filters and blocking. ISPs and corporations are paying close attention to incoming email in the effort to block spam, or unsolicited email. Anti-spam filters scan the from and subject lines of email as well as email body text for certain language. They can also detect mailing patterns, frequency and volume.

Your legitimate, permission-based email could be bounced back to you by a spam filter, or your mail server might be flagged as a potential spam source. In either case, your messages won't make it through.

What can you do? Use an email marketing service with a strong permission policy and an active anti-blocking team. Solid email marketing companies develop relationships with ISPs to be sure their customers' permission-based email gets through. A good email marketing service gets more attention than you could ever get on your own.

Ask your readers to help. If your email is being blocked at a particular company or ISP, ask devoted customers/readers to contact their postmaster and request to have your email "un-blocked."

And Then...?

* Analyze your bouncebacks. If you use an email marketing service, be sure that it categorizes bouncebacks and provides detailed reports that allow you to view and manage bounced email addresses. Take the time to analyze your bouncebacks and remove hard bounces from your list. It should also be easy to correct obvious typos in your list (e.g. ".con" instead of ".com").

* Monitor your "reply to:" address. Many recipients are fearful of using the unsubscribe function, as it has been used by spammers to verify an address, rather than as a legitimate unsubscribe function. So, be alert to unsubscribe requests coming to your "reply to:" address and permanently remove those email addresses right away.

Finally, pay attention to email address change requests coming to your "reply to:" address and honor those in a timely manner as well.

So dude, use these tips, take a look at your falling bounce rates and say it with me: "Sweeeet!"