Servers like that are not good for mailing lists. They may have allowed you to send a lot of email without a reasonable limit, but they also had a bad reputation and much of your email if accepted probably delivered to recipient spam folders. It worked in the earlier 2000's for customers that demanded higher sending limits and didn't care about the results that their lists achieved. At the time EarthLink still had that relay pool listed on their KB site. EarthLink recently merged with Windstream. You'll need to contact Windstream customer service to find out what relay options are currently available for business customers.
For a long time I have recommended sending email newsletters with a service dedicated to that purpose such as
MailChimp.
If you prefer an un-managed solution that lets you "blast" without extras such as email templates, you'll still be held responsible for abuse issues, but a solution such as
dedicated SMTP from LuxSci could work too.