It sounds like you're looking for e-mail newsletter and marketing software similar to the likes of Mailchimp (but libre software).

Mailman is good software and is kept updated, but its underlying design is somewhat dated and whilst it can be used for newsletters its principally employed for e-mail discussion lists.

For e-mail newsletters or marketing, you may want something specifically designed for that purpose with more features. You could self-host phpList, as an example. If you don't want to self-host, they offer a paid hosted service at their .com address.