Personalization: The articles and the news should be personalized based on the nodes that I follow (preferably with frequency weighting).
Organization: If the links to the articles were organized under headings with the node name under which they became popular, it'll be much easier to skim through and click on links in relevant sections.
Jobs: While the jobs section on Hashnode is a very interesting addition, the list could be a lot smaller in the newsletter. I understand that you want to push that feature, but having 7-8 listings on the newsletter defeats the purpose. Having 2-3 listings, accompanied by "Read More" would be more than sufficient and hopefully drive traffic to the webapp as well.
[Update]: Unsubscribe per node: Low priority, super advanced feature. Allow users to unsubscribe a node in the newsletter. For example, I like React, but I don't want notifications about it. OTOH, I love reading more about Spring. Some settings to allow unsubscription per node would be useful once you start following a lot of topics and want a focussed newsletter in the e-mail.