Omnisend Email Marketing & SMS

I use this app to provide a sign-up box on my website, to send email blasts, and to send a sequence of abandoned cart emails. It allows you to segment your audience and even connects to Facebook to create custom audiences/lookalike audiences based on your subscriber list. I haven't had any trouble with the app and cannot recommend it enough. I've been using it for about two years on the paid version (not pro).