Email marketing is more than coming up with catchy subject lines, content, and CTAs. In order to scale out a highly optimized email marketing operation you need to:

• Be capable of creating or sourcing an email marketing template that accommodates the hundreds of browser / client combos.
• Understand the fundamentals of responsive email design.
• A/B test your emails.
• Understand how your emails are integrated with reporting and analytics.
• Craft emails with personalization in mind.

You need to do a million things outside of sending out an email with a subject line, content, and a cta.