More online retailers are attempting to win back shoppers who start a purchase and walk away without completing it.

That’s according to a new report from email marketing vendor Listrak, which looked at the 2015 email marketing habits of the 1,000 retailers in Internet Retailer’s 2015 Top 500 Guide and Second 500 Guide. Listrak’s data shows that 35.2% of the 1,000 largest online retailers in North America follow up with at least one email after a customer abandons an online shopping cart, up 5.1% from 33.5% of all retailers in the Top 1000 that did so in 2014.

Broken down further, a growing number of smaller retailers made more of an effort in 2015 to get customers who walk away from an online purchase to come back to their site. Listrak reports that 35.4% of retailers in the Second 500 sent at least one email to customers who abandoned their online shopping cart, up 8.3% from 32.7% of online retailers in the Second 500 who sent at least one shopping cart abandonment email in 2014. The year-over-year growth rate for retailers in the Top 500 was lower. 35% of retailers in this year’s Top 500 sent at least one shopping cart abandonment email, up 2% from 34.3% of online retailers who sent one the year before.

“While each year we found that more and more top retailers were adopting SCA (shopping cart abandonment) programs and using them more effectively, each year we still found a surprisingly significant number of top retailers not taking advantage of this powerful retargeting opportunity, and of those using SCA, many who were not optimizing results with proven best practices,” Listrak says.

Shopping cart abandonment emails have higher open rates (24.9% versus just under 15%), click-to-visit rates (26.9% versus slightly more than 10%) and conversion rates (19.7% versus just under 10%) than basic marketing messages, Listrak’s data finds.

Not only are more retailers emailing shoppers who abandon carts, they’re doing so with greater frequency. Listrak says 9.5% of online retailers in the Top 1000 sent four or more shopping cart abandonment emails to each customer who abandons a cart, up 31.9% from 7.2% of all retailers last year. The percentage of retailers sending at least two shopping cart abandonment emails to each customer who abandons a cart also grew, with 25.9% sending more than one this year, up 15.6% from 22.4% of all retailers last year.