While there is no universal best day or time of day to send an email, you can determine what works for your company, based on your audience and industry.
Use your campaign reports to follow subscriber open rates. If you send multiple types of emails, each type should be considered independently of the others.
You’ll need at least 10 to 15 campaigns in order to start comparing results. Start comparing open rates each day to see if a trend appears. Do consumers like to receive promotions on Sundays, for example?
Remember, your campaign calendar is unique to your company. Consider your audience, their schedules, and any environmental factors that affect them in order to compile your full email timeline.