Usenet works much the same way these days. Using and choosing vendors depends on the vendor's ability to survive economically. Choosing a vendor because there is no charge for their services is the highest form of folly. The Internet is home to about 50,000 mailing lists on a huge range of subjects. Each list has between 10 and 10,000 subscribers.
Mailing lists vary significantly in frequency, content, tone and local culture.
You send a piece of mail to the mail software and it distributes it to the rest of the group. The names refer to the software that operates the list. That's important because your ability to research the membership of a list depends on using the right instructions. Each piece of mailing list software has a different set of instructions. You can review many listserve groups by email.