• by George Bilbrey , Op-Ed Contributor, September 1, 2010

For over a year now, email deliverability experts have been talking about the 'fact' that ISPs use engagement metrics (typically not defined by these so-called experts) to determine inbox placement. But calling it a fact is a bit misleading given that none of the large mailbox providers has talked publicly about if they use engagement metrics to determine where emails get delivered.

But that will soon change as Microsoft is in the early stages of utilizing user behavior when determining individual-level inbox placement for Windows Live Hotmail. That means that an individual user's behavior can influence the delivery of a message from a particular source for that user only. The individual-level analysis overrides the global spam filter's decision. As a result, the way one user interacts with messages from a certain source might influence Hotmail to put those messages in that user's inbox, whereas the way another user interacts with the same messages might influence Hotmail to put those messages in that user's junk folder, regardless of what the global spam filter suggests.

I believe this is mostly good news for email marketers, as now filtering can be done at the subscriber level in addition to the global sender reputation level.

So, what metrics are being analyzed to determine interaction? It's important to note that clicks are NOT a metric in the mix. But Hotmail is looking at a large number of metrics including:

• Messages read, then deleted
• Messages deleted without being read
• Messages replied to
• Frequency of receiving and reading a message from a source

Consider the Hotmail user who frequently deletes messages from a particular source without reading them, based on a quick scan of the subject lines. But occasionally this user gets a message from that source and reads it right away. In this case, Hotmail will be inclined to put mail from that sender to that user in the inbox.

According to Microsoft, the primary scenario for using this type of data is to reduce false positives. If global rules would put a message into the junk folder, but a particular Hotmail user has interacted positively with messages from that source, Hotmail will inbox the message for that user. The data could also be used to put messages in the junk folder where the global rules would have inboxed it, but that is a minority case right now. Also, Hotmail will send Certified email into the inbox, even where those individual metrics might have indicated placement in the junk folder. [Disclosure: My company, Return Path, provides Certification services to Microsoft for all of their email services.]

It's worth noting that if a user blocks a message from a particular source, that will override the user behavior triggered filtering. Direct consumer preference will always be honored, as it always has been.

What should marketers do in light of these changes?

1. Use a seed list based system to monitor your deliverability: You may have heard that seed lists won't work when ISPs use individual level filtering. This is pure nonsense. Seed lists will tell you what they have always told you - how your email gets delivered based on the global filtering rules and with the usual level of filter setting. This is still vital information to understanding how your email is viewed and treated by ISPs. Global filtering still applies for all senders, for all mailbox providers globally.

2. Analyze and respond to activity by your subscribers: Stop sending email to subscribers who never respond. Really. It's not getting you anything and it is clearly going to start hurting you, at least at Hotmail and probably elsewhere. A recent Return Path study found a stunning number of top-brand marketers continued to send high volumes of email to an account that was practically abandoned. Only a handful made any attempt to "win back" these subscribers.

3. Enough already with the batch-and-blast: Irrelevant messages are going to hurt your deliverability even more directly than ever before. Even if they don't generate complaints. Lack of activity and interaction is no longer a neutral metric -- it now has a cost.

4. Meter frequency and cadence based on subscriber preference and behavior: This might mean less email for some subscribers. Yes, really. Unless you are sending the hottest, can't-wait-just-gotta-open-it daily news feed email you are going to hurt yourself by continuing to send high volumes of email to everyone. For most email marketers, the activity metrics can't possibly keep up. Finding the happy medium where you send enough email to keep subscribers interested and active, but not so much that they grow numb and tune out, is going to be the new imperative. Do that at the subscriber level to optimize your opportunity.

Microsoft will discuss these and other changes in more detail in an upcoming call with the Email and Service Provider Coalition and on their own blog. We'll update the Return Path blog with additional information and insights as we get them.