NEW YORK ( TheStreet) -- Shoppers fell prey to flashy store emails on Cyber Monday.

Emails drove 23.9% of orders on Monday, considered the busiest online shopping day of the year, based on data from marketing and analytics firm Custora, which tapped its index of 100 online retailers, accounting for 100 million shoppers.

Last year, emails accounted for a higher 27.7% of orders on Cyber Monday. But these figures eclipse the 16% of daily online orders emails drove on average from January to October of this year, Custora data show.

"Emails are a lot more relevant on Cyber Monday because they include discounts, so people know they can find good deals upon checking their inbox," says Corey Pierson, Custora's CEO. "The challenge with email is to be relevant, but it's easier to be relevant on Cyber Monday rather than a random Monday in the middle of the year where people are checking their inbox to email friends."

Emails proved more effective than other marketing channels, including paid search, organic search and social media. Email marketing was even more popular on Black Friday, driving 27.3% of orders.

"Every retailer I talk to tells me that the response rate on directed emails is extremely high and that emails are extremely cheap to use versus other methods of contacting the customer like, broadcast, print, or direct mail," says retail expert Jan Rogers Kniffen, CEO of J. Rogers Kniffen WWE. "I cannot imagine that email and text messages will not become the primary way of contacting the customer, if it hasn't already."

Beyond emails, overall revenue on Cyber Monday jumped 15.4% compared to last year, Custora data reveal. Additionally, data gathered by Adobe found sales rose 17% to $2.68 billion, a record for Cyber Monday.

"This is what the retailers were looking for," Pierson adds. "This is part of a general trend, as more and more commerce is shifting online and on Cyber Monday, that's as evident as any other time of the year."

Plus, some retailers offered discounts on Sunday, cannibalizing Monday's sales. But that didn't stop consumers from showing up on Cyber Monday. "The discounts were spread out across the weekend, but we still saw strong growth on Monday," Pierson says.

All eyes were on Cyber Monday amid lackluster consumer spending over Thanksgiving weekend, which fell 11%, according to the National Retail Federation.

--Written by Scott Gamm in New York.

More from Opinion

Red Hat CFO Tells TheStreet: Tech Trends Are Still in Our Favor

Red Hat CFO Tells TheStreet: Tech Trends Are Still in Our Favor

Throwback Thursday: Intel Edition

Throwback Thursday: Intel Edition

Intel's Next CEO Should Try Harder to Protect Its Flanks Against AMD and Others

Intel's Next CEO Should Try Harder to Protect Its Flanks Against AMD and Others

3 Warren Buffett Stock Picks That Could Be Perfect for Your Retirement Portfolio

3 Warren Buffett Stock Picks That Could Be Perfect for Your Retirement Portfolio

Wednesday Wrap-Up: GE and Facebook

Wednesday Wrap-Up: GE and Facebook