Listmonk - Send e-mail campaigns from a powerful dashboard. High performance and features packed into one app.
HEY - Email at its best, new from Basecamp.
Sendy - Sendy is a self hosted newsletter app that sends emails 100x cheaper via Amazon SES
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
MailChimp - MailChimp is the best way to design, send, and share email newsletters.
InstAddr - Disposable email address application.