Based on our experience, and on our client's experiences, the best days to send out your newsletters are Tuesdays and Wednesdays. Why? Let me explain:
Mondays people are just coming back from the weekend, and they probably have lots of emails to check, so they will only read the really important ones and eliminate the rest. Thursdays people are in a rush to turn-in reports, or important things that are due at the end of the week. Lastly, Fridays everyone will want to rest of a really hard week, and are anxiously waiting for the weekend.
When is the best time to send out your emails? According to Matt O' Laughlin, Marketing Business Analyst Act LLC, it shows that the best time to send out the emails is between 8am and 9am. In the studies that he made, it showed the majority of the clicks were made that timeframe.
You can see when the best time to send it is for you. Simply look at the statistics that have and compare which days you have sent out, and at what times you have been sent. That way you will be able to see when the best results are.