Mailchimp

Mailchimp predates most newsletter-specific platforms by a decade and is still one of the most widely used tools for sending email at scale. It wasn't built with "newsletter as a media product" in mind the way Substack or beehiiv were — it's closer to general-purpose email marketing software, with campaign templates, list segmentation, and reporting that a lot of small businesses already use for order confirmations and promotions.

For a newsletter, that broad focus can be a strength or a limitation depending on what you need. You get a mature, well-documented platform with solid deliverability and a huge integration ecosystem, but the interface and pricing are built around marketing teams rather than solo writers, so it can feel heavier than a tool designed specifically for publishing.