Litmus recommends around 50 characters. Yes Lifecycle Marketing says emails with subject line up to 20 characters have ethe highest average open rate, unique click rate, and click-to-open rate. An analysis from Retention Science found that subject lines with 6 to 10 words results in the highest open rates. And Return Path advises using 61 to 70 characters.
After you have entered your "List Name" you will need to enter a "List Description." Here is where you will describe the kind of information you'll be sending from this list. There is a 400 character limit for the "List Description." Subscribers will see your "List Description" on the unsubscribe page if they ever go to unsubscribe from your list. Once you are done entering your "List Description" click the "Next Step" button.