Coming up with an engaging subject line is one of the hardest parts of email marketing. The subject line determines whether the email gets opened — and whether the whole campaign works. The good news: AI can help generate dozens of creative subject lines in minutes. In this article, we'll cover how to use AI to generate email subject lines and which tools work best.

1. What tasks can AI handle?

  • Generating headlines (subject lines)
  • Generating preheaders (preview text)
  • Generating A/B test variants
  • Suggesting creative angles (emotion, intrigue, benefit)
  • Optimizing wording for a specific audience

Example: an AI can generate 10 variants of a “Sale” subject line with different angles: “Today only!”, “Your personal chance”, “-50% off everything until tonight.”

2. Which tools should you use?

  • ChatGPT / GPT-4 — a versatile assistant for generating text.
  • Jasper — an AI marketing platform with email subject line templates.
  • Copy.ai — a specialized tool for generating headlines and copy.
  • Phrasee — a service optimized for email marketing (generates subject lines with CTR in mind).

3. How do you write a good prompt?

  • Describe the audience (for example: “subscribers of an online clothing store”).
  • State the goal (for example: “increase the open rate of a sale email”).
  • Set the tone (for example: “humorous”, “emotional”, “intriguing”).
  • Ask for 10–20 variants so you can pick the best ones.

4. How do you choose the best variants?

  • Check that they match your brand's tone.
  • Pick the 2–3 strongest variants.
  • Run an A/B test — AI can help, but your real audience decides what works best.

5. How do you automate the process?

  • Create a prompt template that you use for all campaigns.
  • Set up an integration with AI tools via Zapier or an API.
  • Build a database of successful subject lines so the AI can suggest similar ones.

Common mistakes

❌ Blindly copying every AI-generated variant → it doesn't always match your tone.❌ Using only one angle (for example, only intrigue) → it's better to test different angles.❌ Not checking the results → CTR matters, not just the number of generated subject lines.

Conclusion

AI is a powerful tool that can:✔ save you time,✔ breathe fresh ideas into your campaigns,✔ help you find the best options faster.