Common Email Segmentation Mistakes in the Mobile Inbox Era
Why segmentation built for the desktop inbox was breaking down in 2013, as mobile opens climbed past half of all email and Gmail's tabbed inbox landed.
The segmentation mistakes that mattered most in 2012, buying lists, ignoring behavior, never sunsetting inactive contacts, hadn’t gone away. But 2013 introduced a new set of problems, driven by two changes outside any marketer’s control: mobile email finally overtook desktop, and Gmail rolled out tabbed inboxes to its entire user base. Neither shift was optional to plan around.
Mistake 1: ignoring device in your segments
By 2013, industry reporting from email vendors like Litmus was showing mobile opens closing in on, and in some lists surpassing, half of all opens. A segmentation strategy built entirely around desktop behavior, long-form content, dense multi-column layouts, was now failing a growing share of recipients before they even finished loading the email. Segmenting by primary device, and sending mobile-optimized creative to that group, stopped being a nice-to-have and became table stakes.
Mistake 2: not accounting for the Gmail Promotions tab
Gmail’s tabbed inbox, which separated Primary, Social and Promotions, rolled out broadly in 2013 and changed what an “open” meant. Marketing email that used to land in the primary inbox was now routed into Promotions by default for most Gmail users, and engagement on lists heavy with Gmail addresses shifted accordingly. Segments built on historical open-rate benchmarks from before the rollout were comparing numbers that weren’t measuring the same thing anymore.
Mistake 3: segmenting on open rate alone in an image-blocking world
Most inbox clients still blocked images by default in 2013, which meant open tracking, which typically relies on a tracking pixel loading, was undercounting actual opens across a meaningful share of any list. Teams that segmented purely on “opened in the last 90 days” were quietly misclassifying engaged subscribers as inactive. Click behavior and other explicit actions became a more reliable signal to segment on than opens alone.
Mistake 4: never testing segments across clients and screen sizes
A segment that performs well in testing on one email client can perform differently once it reaches the mix of clients an actual list uses, Outlook, Gmail, Yahoo Mail, and a growing list of mobile apps, each rendering HTML differently. Skipping cross-client testing before sending to a large segment meant some subscribers received broken layouts without anyone on the team knowing until replies or complaints started coming in.
Mistake 5: letting segments go stale
A segment built from a snapshot of list behavior six months ago doesn’t reflect who’s engaged today, especially with device usage and inbox behavior both shifting as fast as they were in 2013. Segments need a refresh cadence, not a one-time setup, or they end up targeting a version of the list that no longer exists.
The lesson from 2013 wasn’t that segmentation strategy was wrong. It was that the inbox itself was changing fast enough that strategies needed to be revisited more often than most teams were used to, and that a segment defined purely by demographics or a stale engagement window was going to miss more of the list with each passing quarter.
Keep exploring: browse more Email Marketing guides, see everything we published in 2013 or check out the Digital Business Marketing Awards.
