Being the CEO of Click A Tree, we use MailerLite which is the best email marketing software.
They offer all the features you need, including segmentation, automation, A/B testing, auto-resend, time-zone scheduling and so on. They even have a website builder, landing page builder, WordPress plugin and everything else you need to own the web.
Up to 1,000 subscribers are free on their starter plan, so as a small company you can try them out risk-free. Over 1,000 subscribers they offer the fairest rates in the industry.
Especially outstanding is their customer support, which many competitors like MailChimp don't offer - or not as good. When you contact their service department, you always receive an answer within hours, no matter which time zone you're in. Since MailerLite works as remote team, they also cover many time zones, and hence someone is always awake when you are.
We've been using them for several years now (I think it's about 3 years)