The question I am most often asked is, "When is the best time to send an email?" The answer (you're going to hate this): It depends.
It depends on whether your readers prefer to read emails before work, at lunchtime, during the afternoon slump, in the evening, or just before bedtime. Are they nightowls or insomniacs? Are they in different time zones?
Is it better to send emails at popular times, when people are online, or will your message just get lost in the shuffle?
Is it advantageous to send an email when others aren't (3 a.m.?), so you get the top spot in the Inbox?
Also be aware that open rates vary by industry. For example, real estate mailings sent on Fridays do well, as prospective buyers plan what open houses to visit over the weekend. Email service providers such as Constant Contact and Mailchimp provide guidelines on best times to send by industry.
Just for fun...last year I did a little research. Here are my notes, in very rough form, as I never intended for anyone else to see them. Warning: your head might spin reading the conflicting advice.
Best practice? Take your best guess. Tuesday at 10 a.m. is a safe bet. Then review the data on what days and times people are actually reading your emails and adjust accordingly.
Helping small businesses increase sales and nonprofits increase donations by engaging with customers through email marketing and social media.