Amazon.com Inc. sent more than 1 billion promotional emails to consumers in the run-up to, and on, Prime Day (July 11,  a Tuesday), and consumers paid attention.

Daily average open rates exceeded 20% on all but one day (July 9, a Sunday averaged 13%), according to eDataSource, which tracks retailers’ email marketing campaigns. The highest daily average open rates were on July 2, 3 and 5, at 16%, 25% and 28%, respectively.

Compared with last year, open rates were somewhat lower in the early stages of the promotion period, which began June 29 and ran through Prime Day, and somewhat higher in the mid to late stages, eDataSource says. This pattern may be due to greater public awareness and a high volume of media coverage of Prime Day, says says John Landsman, director of strategy and analytics for eDataSource. “Customer anticipation definitely built this year to an even greater degree than in the past, and related emails closer to the event itself may be pulling higher engagement as a result,” he says.

Amazon sent 68 email campaigns on Prime Day, a 70% jump from the 40 campaigns it sent a year ago. Those 68 campaigns totaled 398 million messages, eDataSource finds. On the day before the sales event, which included six hours of Prime Day sales, Amazon sent 27 campaigns that totaled 335 million messages.

Campaigns that had a lower send volume to a more targeted audience tended to have higher read rates. For example, a June 30 email send of just 30,000, with a subject line, “2017 Prime Day Announcement: Get Your Account Ready!” had a 50% open rate. In contrast, the June 29 kickoff email to 72 million consumers, with the subject line of “Prime Day returns July 11,” had a 17.9% open rate, according to eDataSource.

Amazon’s maximum open rates—a maximum rate is the that of the top-performing campaign on a given day—on Prime Day-related emails were “really enormous” and “much larger than we typically see with other retail brands,” Landsman says. The highest maximum rate was 64% on July 6, followed by 58% on July 5 and 53% on June 30.

“Amazon’s overall open rates on retail-related promotional emails tend to be in the mid-20% range, more or less consistent with those seen for this year’s Prime Day-related emails,” Landsman says. Amazon’s open rates are consistently much higher than those of other retailers because of “the extreme precision with which Amazon targets its emails and populates them with relevant, personalized content,” he says.

The e-retailer directed almost a quarter, or 265 million, of its nearly 1.1 billion Prime Day emails to India. It was the first year Amazon held Prime Day in India, which has a “massive email audience,” eDataSource says in its analysis. Even without India, Amazon sent significantly more emails than last year, it says.

The third annual Prime Day was a 30-hour event in 13 countries, with the sale starting at 6 p.m. Pacific on July 10 and running through midnight Pacific on July 11. Internet Retailer estimates Amazon, No. 1 in the Internet Retailer 2017 Top 500, sold $2.41 billion worth of goods, up 58.6% from $1.52 billion from last year. The Prime Day total is roughly 325% more than what Amazon sells on an average day, Internet Retailer finds. Amazon does not release Prime Day sales numbers.

Amazon was not the only retailer promoting sales on Prime Day.

An Internet Retailer analysis of the 100 largest non-Amazon online retailers in North America found that 47 tried to capitalize on Prime Day attention by offering a limited sale on July 11 or using “prime” in emails. Data from Salesforce.com Inc. Commerce Cloud, formerly known as Demandware, found that online sales for non-Amazon retailers increased 44% year over year on Prime Day.

When looking at total online shopping traffic on Prime Day, Amazon captured the vast majority of it, according to data analytics firm SimilarWeb Ltd. Amazon had 113.2 million visits to its site on July 11, a 49.1% increase from traffic on Tuesday, June 27. This increase also represented the largest growth in traffic compared with other online retailers, although Macys.com was not far behind with a 47.2% increase in site traffic on Prime Day compared with June 27.

Macy’s Inc. (No. 6 in the Top 500) sent 30.6 million emails with “Black Friday in July” in the subject line on Prime Day, generating a 16.3% open rate, according to eDataSource.

Other retailers’ Prime Day emails were as follows, eDataSouce says:

• Walmart (No. 3) sent 30.3 million “Huge Summer Savings” emails on July 11 and had an 8.5% open rate.
• Staples (No. 5) sent 5.0 million emails with “Up to $210 off on select laptops, desktops & more” and had a 13.6% open rate.
• Best Buy (No. 9) sent 38.2 million emails touting “Big Deals Day” and had an 11.2% open rate.
• Kohl’s (No. 18) sent 19.3 million emails with the subject line “Only a few hours left … 30% off” with a 10.2% open rate.
• Sears (No. 19) sent 15.2 million emails with a subject line of “Exclusive online deals” and had a 14.0% open rate.
• Target (No. 20) sent 33.0 million emails tagged “40% off bed and bath refreshers; Tuesday only” and had a 12.1% open rate.
• J.C. Penney (No. 33) sent 13.6 million emails featuring “Cyber Deals” in the subject line and had a 13.9% open rate.