In my newsletter I report about current or past highlights. From time to time I also address important topics about photography. In general, these are purely informative articles, i.e. no sales promotion etc.
As a rule, the newsletter is sent 1 to 4 times a year. Depending on the available time, the newsletter will be a little more detailed or concentrated in its content 🙂
I use MailChimp where also the mail address and possibly further information about the sending and analysis of the newsletter are stored.