Email open rates improve by 57% with just one word.

The effect using one of these words in the subject line will have on the email open rate.

Free in favour: +2%

Bonus: +26%

Priority: +79%

Gratitude: +57%

Rejected: -40%

assisting: -12%

Give: -56%

The time is now -45%.

Source: Blog.mailchimp.com