Are there any good and convenient free scripts for mailing lists?

Question

Computer networks

Are there any good free scripts for organizing mailing lists from the site? There are a lot of subscribers - about 20,000. All are customers of the store. The mailing module in the store itself is frankly inconvenient, so I thought about changing to a normal tool. But it is necessary that simple managers could use it.
I do not want to use third-party services, because we have our own server, our own clients, and we don't want to give our base to someone, especially since I'm not sure that this base will not go hand in hand later.

Answer 1

Google to the rescue

Answer 2

Check out this janicky.com/php-scripts/pochtovaya-rassylka for small corporate mailing lists, it's convenient and takes 2 minutes to set up.