Is it automated by some algorithm (e.g. views/votes/etc...)? Random? Random after selecting for some factors? Manual by moderators/someone else?
Adapted from this answer:
The newsletter includes a brief summary of:
- The Top New Questions of the week (most views, answers, and votes this week)
- Some selected highlight questions from previous weeks.
- Some selected unanswered questions from the past.
These are all automatically selected by the Stack Exchange system.
They may also occasionally contain important announcements from Stack Exchange staff and moderators.
Also see the original annoucement of the newsletter.