It's hard enough to get into Hotmail's inbox these days. Since Hotmail/MSN/Live all started using user engagement metrics and paying closer attention to domain reputation as opposed to IP reputation, the hardest place to not be junk mail has become ... the super hardest place to not be junk mail! And things are about to get even more difficult, because, according to ReturnPath, Hotmail has started using user behavior to over-ride the global spam filter settings. What does that mean?

It means that you may be primed for the inbox and ready for deliverability, but if an individual user hasn't been receptive to your messages, by which Hotmail means that they've deleted them without being read as an example, your message is going into the junk folder for that individual user. So while you may end up in the inbox for some of your seed addresses, it doesn't mean that you're ending up in the inbox for some of your less engaged users.

And, because user engagement stats are such an important part of email deliverability these days, if you keep on sending to those less engaged users, it will ultimately start to hinder your overall deliverability metrics.

What's the key? You need to start pruning non-responsive email recipients off your list. Don't send frequently to long-term lapsed users or unconverted sign-ups. Their low response rates will ultimately keep you from getting into the inbox long term. If you're using email sending software that's worth anything at all, then start to identify your non-opening recipients and remove them from your most frequent sends. Trust us, with the changes in the rankings given to user engagement with email, it is not worth it to continue sending to them in hopes that they'll eventually open and respond.

And, most importantly, get your users into a secondary communications channel, by which we obviously mean a social media channel. Email inbox deliverability is shakier than ever. Have a backup channel ready!