Not all bounces generate the standard “mailer-daemon’ e-mail response we’re used to seeing in our inboxes, but nearly generate a response code in your SMTP log files. These are the files that keep track of every conversation between your e-mail server and receiving servers.
A high bounce rate can have a negative impact on your overall delivery rate. This can, in turn, affect all of your e-mail campaigns, not just the newsletters triggering bounces. If your IP address is associated with too many “unknown user” bounces at a particular ISP, you risk being blacklisted or blocked by that ISP. Therefore, keeping your list clean of unknown users is a cornerstone to your e-mail delivery success.
Whether you send e-mail inhouse or through an e-mail service provider, your bounce-management process should reflect how often you e-mail, the size of your list and the nuances of bounce reporting.
Specifically:
Set “bounce rules”— You need to define how many bounces you will incur before removing an e-mail from your list. The standard rule is that an e-mail should be removed after two “unknown user” hard bounces or three soft bounces over a period greater than fourteen days. An “unknown user” hard bounce indicates that the mailbox no longer exists. A soft bounce could be an “I’m busy, come back later” error. The time period for removal varies, based on how often you send mail. If you mail daily, for example, you can tolerate more bounces than if you mail monthly.
Define a “bounce” with subscribers in mind— Some e-mail platforms can inadvertently categorize a temporary e-mail account status, such as “out of office” replies as a hard bounce. This can lead to unnecessary removal of e-mail addresses from your list. Just because someone doesn’t want to read your e-mail while they are vacationing on the beach, it doesn’t mean they won’t want it once they return. One solution to this phenomenon is to allow subscribers to put mailings “on hold” through an option in a preference center, just as they might stop having their newspaper while out of town.
Manage bounces by ISP—While your overall bounce percentages are good to know and understand, problems will be uncovered faster if you look at your bounces by ISP. A bounce rate of 4% or 5% across your whole list is not too troubling. However, if the majority of those bounces all come back form one ISP—and if they represent the majority, or even the totality, of the e-mail addresses you have for that ISP—this indicates a problem beyond normal e-mail churn. While free accounts (such as yahoo! And hotmail) will have a higher churn rate than paid accounts (like AOL and Earthlink), your bounces should be fairly even across ISPs and should stay consistent from campaign to campaign. By breaking this information down by ISP, for every campaign, you will pick up on deliverability problems much more quickly.
Look beyond the obvious—The bounces you see are one thing, but the information you don’t see can be of even more interest. There is a wealth of information about each bounce response in your SMTP log files. These files record every conversation between your server and the receiving e-mail servers (e.g., ISPs). When your e-mail is blocked, the log files often reveal why. Analyzing these files can point to problems you are having at particularly mail servers. For this reason, make sure that you, your IT team and your e-mail deliverability experts are reviewing them on a regular basis.
Remember that blocks and bounces are not the same—If you remove an address from your file because of a general ISP blocking message, you will be removing a potentially good customer. Make sure you separate true bounces, where the e-mail address is no longer valid, from messages that indicate that a valid address is being blocked by the server, and treat them differently. When you resolve a block, re-mail to your subscribers at that domain to confirm that delivery has resumed.
Matt Blumberg and Michael Mayor are the driving forces behind Return Path, an e-mail performance company. Collaborating with them on this project are their colleagues, e-mail strategists Stephanie A. Miller and Tami Monahan Forman. This article was excerpted from their new book, “Sign Me Up! A Marketer’s Guide to Creating E-mail Newsletters That Build Relationships and Boost Sales (iUniverse Inc., 2005) © 2005 Return Path, Inc. All rights reserved.
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