First, the emergence of the "social inbox" will give email users more control over which mail they see. Whereas in the past marketers were focused on getting their emails placed in the inbox rather than the junk folder, in the future, marketers will be much more focused on getting their emails among their subscribers' "favorites." That may simply entail getting in their email address added to subscribers' address books, but it may even require an action beyond that. Not being "favorited" will mean that your emails are dumped in with rest of your subscriber's non-spam -- just one tiny step up from the junk folder.

 And second, ISPs are starting to look at customer-level engagement metrics to help determine blocking and inbox placement. Have a lot of disengaged subscribers? That could soon hurt your ability to deliver email to your engaged subscribers. On top of that, ISPs are moving to domain-based reputations, so if you've sullied your reputation on one IP address, you won't be able to just change IP addresses and start over fresh. 

Those changes will likely require to a number of adjustments to be made by email marketers over the next two to three years:

 More sign-up transparency. Fine-print sign-ups during sweepstakes, hidden pre-checked opt-in boxes during checkout, and other sneaky mechanisms for growing lists will become too risky because they will hurt engagement metrics in addition to boosting complaints and unsubscribes. Also, not setting expectations around frequency will also be dangerous, as that's one of the top reasons folks unsubscribe or tune out. The last time I looked at frequency transparency during sign-up, only 4% of major online retailers were upfront with that information -- and that percentage was down from 7% in 2007.

More subscriber control through preference centers. In the future, a well-developed preference center will be critical to delivering tailored, relevant messaging at a frequency that's acceptable to subscribers. While it's becoming more common to be presented with the option to opt-down on an unsubscribe page, it's still incredibly rare for subscribers to be given frequency control at the beginning of the relationship. This will change.

 More and better segmentation and use of dynamic content. The percentage of promotional emails that are purely broadcast will decline in the years ahead because of lackluster performance. Marketers will need to use expressed preferences and behavioral data (purchase history, clickstream data, etc.) to segment subscribers and send them targeted emails, and emails with dynamic content that's specifically user-tailored.           

Greater risk from inactives. The changes that are manifesting may soon tip the scales decidedly toward the camp that recommends cutting inactives from your list. There will be a need for more sophistication around accurately identifying inactives and trying to reengage them.  

More triggered messaging. Transactional emails, browse-based emails, shopping cart abandonment emails, birthday emails and the like -- all will increase in importance going forward because of the higher level of engagement that subscribers have with these emails. An array of triggered emails that address all stages of the customer lifecycle will be vital.

 Some of these program changes will require painful operational mindset shifts, in addition to needing technology outlays. It will take time to make the necessary adjustments to remain competitive in the engagement-reputation Era. Consider this your early warning.