I have been using email marketing for over 14 years. It is the cornerstone of my business. I have only used a handful of email service providers including Constant Contact, MadMimi, and finally switched to ConvertKit. I have been using ConvertKit now for over 2 years and love the automations and option to resend to increase my open rates. Think of ConvertKit like tipping over dominos. When your customer signs up for your freebie, let the automations "dominos" of ConvertKit move them through your email sequence.