On the first look, both sort of media are sounds the same. Sometimes a blog is described as a website while a newsletter is send in the plain text format. But suppose, the newsletter is published in a Blog, there is no visible difference.
But a blog is very different from a newsletter. I would like to explain the details. A blog is something which is created by an individual. Oh i see, this definition doesn't work, because newsletters are created by individuals as well. So it seems, that it's easier to say what the shared principle is over the difference. Perhaps we should go a step backward before the internet age and using pen and paper as the prefered tool. Suppose somebody writes an essay about a topic he likes, for example he invents a short story. This is called a blog. The public won't have any interested in reading such information.
In contrast, a newsletter is created with a different target audience. No, this definition is also not correct because a newsletter can be addressed as a single person as well. I see, it's very hard to define what the difference is. Let me give a third trial.
A blog is feed by a single person, a newsletter is feed by a community. Even if a single person has created the newsletter he is using the input of a larger group. A newsletter is similar to a blog aggregator. Which means that RSS streams are mixed together. The newsletter is not discussing a certain topic, but it explain about which topic the community is talking. A typical example for an entry in a newsletter is, to explain that in the last week the stackoverflow community has solved a major problem in C++. The question is not which kind of problem they have solved, but the news was, who has discussed the issue.
A newsletter is about the social status of group members. It has to do with projects who are done by many. A newsletter is a typical management tool it is used to control larger amount of groups. If somebody questioning if a newsletter is right he is asking about a social structure, management and projects. This explains why newspapers and TV news have an important role into modern society. They are not only posting information, but their role is to manage groups. The funny thing is, that so called alternative newsletter have the same job. They are not an alternative to the newsletter concept but they are trying to manage groups in a different way.
The only real alternative to a newsletter is normal information which is not provided on a meta level but it is going into the details. If in a paper it's written down that 1+1=2 then this information stands alone. There is no need to ask which group is interested also in this problem. An important criteria for a newsletter is, that it's depended on time ad location. All newsletter are grounded at a certain date and a certain place. A typical ticker message starts with the introduction, “According to the embedded journalist in the sims 4, who is sitting in the garden, the party on monday was great”.
A typical example for a newletter was posted to the reddit community. The user has announced that he has build his first house which is a caffe and a techstore in the same building. https://www.reddit.com/r/thesims/comments/a8erpb/built_my_first_house_in_the_sims_4_today_a_caf%C3%A9/ The posting has become 58 upvotes so far, and there is need to forward this story to Wikinews to put it on the frontpage of the new issue. If the journalists at Wikinews are doing their job well, they will verify the source first and ask the Original poster for a small interview in which he can explain the details. For example the question is open if the house contains of two floors or only one.