Specifically, CTO rates declined by 12.6% from the third quarter to the fourth quarter of 2016, while they were down 14.4% year-over-year.
In response to receding CTO rates, marketers need to rethink their strategies, according to Michael Fisher, president of Yes Lifecycle Marketing.
"Tactics like responsive design are no longer enough to spark engagement,” Fisher notes in a new report. "Marketers need to pay attention not only to the design of mobile emails, but now, even more so, the content and context.”
More broadly, Fisher believes email continued to drive revenue for brands during the holidays -- especially on mobile.
More than half (53.4%) of all email clicks came from mobile -- an 8.5% increase year-over-year, and a 31.5% increase since the fourth quarter of 2015, the marketing firm finds.
Also of note, smartphone revenue increased, while the number of smartphone orders decreased, which translates into larger average purchases on smartphones.
In addition, over the past three years, the proportion of email-driven orders placed on smartphones has almost tripled -- and the email-driven revenue generated through smartphones has grown by 250% -- according to Fisher.