You may have heard of "productivity" tips of how on how to tackle your email inbox, but when it comes to email marketing - you must consider the time AND day in order to get the best conversion rate. Remember open rates and click rates are not goals of email marketing.
Your goal is conversion. Even if you have written the best content of your life, you will have low engagement rates if you don't send your emails at the most optimal time.
Smart Insights provides helpful tips (with data to back it up!) on when to send emails.