There have been plenty of studies about the proper send cadence. Determining your send cadence often depends on when your emails are most likely to perform, testing along the way to see what resonates with your audience.
Sending emails two to three times per week seems to be the peak stat. Once per week and four to five times per week both showed associated data trailing off. The data you’re looking for, when it comes to determining a send cadence, involves what keeps your subscribers engaged.