Understand what does and does not occur with bounced e-mail. Once a list gets dirty, it may never get clean again.
I thought the bad old days of poor or non-existent bounce handling were far behind us. Until, that is, I had reason to examine the lists of two companies who were working with other providers. While my examples are specific to e-mail service providers (ESPs) these problems can just as easily arise when using in-house systems, third-party software or delivery appliances.
First, a little history. In the early days of e-mail marketing (the mid- to late 1990s), a major problem was that many senders failed to properly handle notification of undeliverable e-mail, or bounces. There was no compelling reason for an ESP to put a lot of effort into this. There were few, if any, deliverability issues associated with poor bounce handling. The only result of correct handling was that customers' lists shrank. Customers don't like to see their lists shrinking.
These days, too many undeliverable e-mails results in blocklisting. Repeated blocklisting without corrective action causes the undeliverable problem to worsen. Once the undeliverable issue is resolved, the complaint rate skyrockets (as recipients suddenly start receiving messages after a hiatus). That, in turn, leads straight back to blocklisting.
As deliverability began to fall for senders who didn't maintain clean lists, and as deliverability became a high-profile issue, many senders cleaned up their acts. They became much more diligent about identifying undeliverable addresses and ensuring they were removed from future mailings.
When I wrote about bounce handling in January 2005, I thought the only remaining issue was a tendency of providers to mis-categorize failures while trying to identify permanent (hard) and temporary (soft) failure conditions. Unfortunately, it seems the issue runs deeper than that. In addition to mis-categorizing bounces, it appears some are being lost completely, especially in situations where categorization is difficult or impossible.
In analyzing my customers' lists, I found two root causes. In general, both lists were fairly clean except for certain ISPs with exceptionally high bounce and complaint rates. So high, in fact, some parts of the lists are practically unusable. What's exceptional about those ISPs is all did one (or both) of two things that present difficulties for some senders.
Accept, Then Bounce
Most sites will tell you during a delivery transaction whether or not the recipient exists and it will accept the message. However a few sites, for structural or operational reasons, accept messages, then only later send back a failure notification indicating the message is undeliverable.
This presents difficulties for senders. The format and content of the failure notification can be extremely variable. This makes identifying the original recipient and the cause of the failure problematic, or even impossible. Whether senders fail to receive, process, or successfully categorize the bounce messages is impossible to tell. Regardless of which step of the process is failing, the outcome is the same.
Many ISPs now use automated, temporary blocks for senders who fail to meet deliverability or complaint-rate requirements. My analysis indicates some ESPs fail to report these temporary blocks. These blocks present a conundrum. Failure to report them, or reporting them as "soft" bounces, cause blocking again with the next send. On the other hand, reporting a "hard" bounce causes valid addresses to be removed from a list.
There are two steps that every sender can, and should, take to monitor their deliverability.
Analyze Delivery Rates
Monitor your delivery rates for all the major ISPs. Look not just for high bounce rates, but for low bounce, open, and clickthrough rates (CTR) on a per-ISP basis. While it's gratifying it see a low bounce rate, it may actually be a sign of mis-reporting and underlying problems.
Get Independent Verification
Use an independent third party to monitor inbox delivery for your list. Several companies provide this type of service. You add their seed addresses to your list and they tell you how many messages arrived in the inbox, the bulk folder, or weren't delivered at all. This also helps with ISPs such as Hotmail/MSN which are prone to silently dropping suspect e-mail with no notification. Ultimately, this is the only way to be sure your message is getting through and to confirm what your ESP or e-mail group is telling you.
Given the health of your list is important to your business, it's essential to understand what your sender does and does not do with bounces and to verify that what they say is happening truly is happening. Once a list gets dirty it may never get clean again.
Until next time,
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Derek is the managing director of J-Labs, Javelin Marketing Group's technology skunkworks, a role that draws on his 20 years of experience and leadership in the fields of marketing and technology. A British expatriate based in Seattle, Washington, Derek is perhaps better known as the founder and technologist behind Innovyx, one of the first email service providers later acquired by the Omnicom Group. An industry veteran and thought-leader, Derek is a regular expert author, contributor, conference speaker, and takes an active role in a number of industry and trade groups.
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