Email - What Days Have the Highest Open Rate?

Great question! 

If you follow the link to the Marketing Charts article, at the bottom is the following:

Open and Click Rates by Day of the Week

There was less variance when sorting by day of the week (these results not limited to US accounts), although some patterns were apparent. During H1 (first half of the year), email open rates were lowest on Sunday (8.5%), Saturday (9.4%) and Thursday (9.4%), while during H2 (second half of the year), Saturday (6.1%) clearly had the lowest open rate, followed by Sunday (9%) and Thursday (9.6%). While there seemed to be a clear trend for lower open rates during the weekend, the sluggish rates on Thursdays was a fairly curious result.

During H1, open rates were highest on Tuesdays and Wednesdays (each at 10.7%), while during H2, they were highest on Tuesdays (10.7%) and Mondays (10.4%).

Click rates followed a different pattern. While Sundays sported generally below-average open rates, they had the highest click rate during both H1 (2.2%) and H2 (2.6%). Also of note: the next-highest click rates were reserved for Tuesdays (H1: 2.1%; H2: 2.5%), which had the highest open rates, suggesting that drawing conclusions regarding the relationship between open and click rates is a perilous endeavor.

During H1, the lowest click rate was on Monday (1.5%), while during H2, Saturday had the lowest average click rate (1.3%).